We thank B. Konkena und W. Schuhmann for valuable scientific discussions. Financial support by the Fonds of the Chemical Industry (Liebig grant to U.-P.A.) and the Deutsche Forschungsgemeinschaft (Emmy Noether grant to U.-P.A., AP242/2-1).

1. High-temperature Synthesis of Fe 4.5 Ni 4.5 S 8
NOTE: The herein described procedure for the synthesis of Fe4.5Ni4.5S8 is adopted from the literature.8,10 The strict application of the reported heating ramps is of high importance to prevent formation of phase impurities and defects of the silica ampule.
<ol>
	<li>Mix iron (1.66 g, 29.8 mmol), nickel (1.75 g, 29.8 mmol) and sulfur (1.70 g, 53.1 mmol) thoroughly in a mortar and transfer the mixture to a silica ampule (10 mm diameter).</li>
	<li>Evacuate the ampule overnight at 10-2 mbar.</li>
	<li>Seal the ampule and place it in a tubular furnace.</li>
	<li>Increase the temperature from room temperature (RT) to 700 &#176;C at 5 &#176;C/min followed by an isothermal step for 3 h.</li>
	<li>Increase the temperature to 1100 &#176;C within 30 min and keep it isotherm for 10 h.</li>
	<li>Slowly cool the sample to RT by switching off the furnace. Crack the ampule to collect the solid product. Make sure to separate the Fe4.5Ni4.5S8 completely from silica glass fragments.</li>
</ol>
2. Physical Characterization
<ol>
	<li>Mount a 10 mm x 5 mm x 3 mm piece of Fe4.5Ni4.5S8 rock on the sample holder and place in the vacuum chamber of the SEM instrument. Record the SEM images at 650X and 6,500X magnification at 20 kV. Simultaneously, use the same sample for EDX analysis at 4.4 kV.</li>
	<li>For the collection of PXRD data, apply finely ground powder of Fe4.5Ni4.5S8 and mount it on an amorphous silicon wafer using silicon grease. Mount the wafer on the sample holder and collect the data in a continuous scan mode from 10-50&#176; at a scan rate of 0.03&#176; per 5 s using Cu-K&#945; radiation (&#955; = 1.5418 &#197;).</li>
	<li>For M&#246;ssbauer analysis finely ground powder is used and placed in a polyoxymethylene (POM) cup. Record zero-field M&#246;ssbauer spectra at 25 &#176;C using a 57Co radiation source in a Rh-matrix.</li>
	<li>For DSC analysis, finely ground powder is placed in a tared &#945;-Al2O3 crucible. Perform DSC measurements in the range from RT to 1,000 &#176;C recording the heating and cooling curve at a rate of 10 &#176;C/min. Perform the experiment under a flow of high purity nitrogen.</li>
</ol>
3. Preparation of &#39;Rock&#39; Electrodes
<ol>
	<li>Solder a copper wire to a wire ferrule.</li>
	<li>Cut the Fe4.5Ni4.5S8 bulk material into smaller pieces (approx. 5 mm x 5 mm x 5 mm).</li>
	<li>Place the small piece of Fe4.5Ni4.5S8 in the ferrule in a way that approx. 2 mm of material sticks out of the ferrule.</li>
	<li>Mantle the ferrule and copper wire with 100 mm of Teflon tubing.</li>
	<li>Seal the tip of the electrode with two-component epoxide glue and dry the electrode overnight under ambient conditions.</li>
	<li>Grind off the tip until the shiny surface (metallic finish) of the Fe4.5Ni4.5S8 is exposed. Further polish with fine grade sand paper (20, 14, 3 and 1 &#181;m grit) to obtain a smooth surface.</li>
	<li>Clean the surface with deionized water and let it dry on air.</li>
</ol>
4. Preparation of &#39;Pellet&#39; Electrodes
NOTE: Custom-built Teflon casings with a brass rod were used as contact for &#39;pellet&#39; electrodes (3 mm diameter).
<ol>
	<li>Grind 50 mg of material to obtain a fine powder of the Fe4.5Ni4.5S8 material.</li>
	<li>Fill the finely ground powder into a compressing tool (3 mm in diameter) and press the material with a maximum weight force of 800 kg/cm2.</li>
	<li>Remove the pellet from the mold using a distance holder.</li>
	<li>Apply a two-component silver-epoxide glue on the brass rod in the cavity of the Teflon casing. Avoid any pollution of the tip of the Teflon-casing.</li>
	<li>Place the pellet in the Teflon casing. The flat side of the pellet must stick out ~1 mm.</li>
	<li>Remove any pollution on the Teflon casing with a paper tissue.</li>
	<li>Verify the contact between the brass wire and the Fe4.5Ni4.5S8 pellet with a voltmeter to assure proper conductivity.</li>
	<li>After 12 h of curing the two-component glue at 60 &#176;C, cool down the electrode to ambient temperature.</li>
	<li>Polish the electrode with sand paper (20, 14, 3 and 1 &#181;m grit) to obtain a shiny flush flat surface within the Teflon case.</li>
	<li>Clean the surface with deionized water and let it dry under ambient conditions.</li>
</ol>
5. Electrochemical Testing of Electrodes
NOTE: The experiments were accomplished with a standard three-electrode setup using the Fe4.5Ni4.5S8 electrode as working electrode, Ag/AgCl (sat. KCl or 3 M KCl solution) electrode as reference electrode and Pt wire or Pt-grid as counter electrode. A gas-tight cell equipped with a stirring bar was filled with the electrolyte consisting of 0.5 M H2SO4 for all electrochemical experiments. The electrolyte was not exchanged during the electrochemical testing of an electrode. All potentials are referenced to ERHE (RHE = reversible hydrogen electrode) according to ERHE = EAg/AgCl + X + 0.059 pH with X = 0.197 V (saturated KCl) or X = 0.210 V (3 M KCl), unless noted otherwise.
<ol>
	<li>Preliminary steps
	<ol>
		<li>Connect all three electrodes with the wires of the potentiostat.</li>
		<li>Add 25 mL of electrolyte (0.5 M H2SO4) into the electrochemical cell and adjust the electrodes to ensure that the electrodes are fully immersed into solution. Subsequently, switch on the potentiostat.</li>
		<li>Switch on the magnetic stirring.</li>
	</ol>
	</li>
	<li>Electrochemical cleaning of the electrode surface
	<ol>
		<li>Perform a cyclic voltammetry (CV) experiment to obtain fast overview on the electrochemical processes that can be observed.</li>
		<li>Set the potential range from 0.2 to -0.2 V with a scan rate of 100 mV/s (non-catalytic potential area). Further, set the number of cycles to 20.</li>
		<li>Start the cycling process and wait until the last cycle is finished. If at least the last 3 to 4 obtained cycles coincide, the electrochemical electrode cleaning is completed. In case of divergence add more cycles until stable curves are obtained.</li>
	</ol>
	</li>
	<li>Measurement of the catalytic performance &#8211; linear sweep voltammetry
	<ol>
		<li>Before starting the experiment determine the iR compensation value for the electrochemical setup.</li>
		<li>Select the program for linear sweep voltammetry (LSV) experiments and set the potential range from 0.2 to -0.6 V and the scan rate to 5 mV/s, including the iR drop into the experiment. Start the experiment.</li>
		<li>Repeat the linear sweep experiments to ensure reproducibility. In case of non-reproducible results start over from step 5.2.</li>
	</ol>
	</li>
	<li>Stability measurement &#38; quantification
	<ol>
		<li>Perform a controlled potential coulometry experiment (CPC).</li>
		<li>Set the potential to -0.6 V with an experiment time of at least 20 h (72,000 s).</li>
		<li>Simultaneously collect gas samples with a gas tight syringe from the headspace of the sealed cell through a septum for every hour for at least 4 h of the experiment. Inject the samples into a GC instrument for quantification and determine the amount of hydrogen produced using a calibration curve recorded on this instrument.</li>
	</ol>
	</li>
	<li>Estimation of the electrochemical surface area (ESCA) 
	NOTE: Do not stir the electrolyte solution during this experiment.
	<ol>
		<li>Determine the iR compensation to measure the resistance of the solution.</li>
		<li>Select a potential range between 0.1 and 0 V in the cyclic voltammetry experiment and set the scan rate to 10 mV s-1. Use the iR drop correction. Set the number of cycles for the experiment to 5.</li>
		<li>Repeat steps 5.4.1) to 5.4.2) for scan rates of 20, 30, 40, 50 and 60 mV s-1.</li>
		<li>From the obtained CV curves pick the fifth cycle for further interpretation.</li>
		<li>Determine the charging current density differences (&#916;j = ja jc) and plot these values as a function of the scan rate. The linear slope is equivalent to twice of the double-layer capacitance Cdl, which is proportional to the electrochemical surface area (ECSA).</li>
	</ol>
	</li>
	<li>Electrochemical impedance spectroscopy (EIS)
	<ol>
		<li>Record electrochemical impedance spectra in the frequency range from 50 kHz to 1 Hz at the corresponding open-circuit potential and an overpotential of 0.3 V.</li>
		<li>Plot the Nyquist plot from the received data to determine the charge transfer resistance.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>May, M. M., Lewerenz, H. -. J., Lackner, D., Dimroth, F., Hannappel, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficient+direct+solar-to-hydrogen+conversion+by+in+situ+interface+transformation+of+a+tandem+structure.">Efficient direct solar-to-hydrogen conversion by in situ interface transformation of a tandem structure.</a> Nat Comm. 6, 8286 (2015).</li><li>Sheng, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Correlating+hydrogen+oxidation+and+evolution+activity+on+platinum+at+different+pH+with+measured+hydrogen+binding+energy.">Correlating hydrogen oxidation and evolution activity on platinum at different pH with measured hydrogen binding energy.</a> Nat Comm. 6, 5848 (2015).</li><li>Li, X., Hao, X., Abudula, A., Guan, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanostructured+catalysts+for+electrochemical+water+splitting:+Current+state+and+prospects.">Nanostructured catalysts for electrochemical water splitting: Current state and prospects.</a> J. Mater. Chem. A. 4 (31), 11973-12000 (2016).</li><li>Merki, D., Hu, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recent+developments+of+molybdenum+and+tungsten+sulfides+as+hydrogen+evolution+catalysts.">Recent developments of molybdenum and tungsten sulfides as hydrogen evolution catalysts.</a> Energy Environ. Sci. 4 (10), 3878 (2011).</li><li>Kibsgaard, J., Chen, Z., Reinecke, B. N., Jaramillo, T. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineering+the+surface+structure+of+MoS2+to+preferentially+expose+active+edge+sites+for+electrocatalysis.">Engineering the surface structure of MoS2 to preferentially expose active edge sites for electrocatalysis.</a> Nat Mater. 11 (11), 963-969 (2012).</li><li>Kong, D., Cha, J. J., Wang, H., Lee, H. R., Cui, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=First-row+transition+metal+dichalcogenide+catalysts+for+hydrogen+evolution+reaction.">First-row transition metal dichalcogenide catalysts for hydrogen evolution reaction.</a> Energy Environ. Sci. 6 (12), 3553 (2013).</li><li>Voiry, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhanced+catalytic+activity+in+strained+chemically+exfoliated+WS(2)+nanosheets+for+hydrogen+evolution.">Enhanced catalytic activity in strained chemically exfoliated WS(2) nanosheets for hydrogen evolution.</a> Nat Mater. 12 (9), 850-855 (2013).</li><li>Konkena, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pentlandite+rocks+as+sustainable+and+stable+efficient+electrocatalysts+for+hydrogen+generation.">Pentlandite rocks as sustainable and stable efficient electrocatalysts for hydrogen generation.</a> Nat Comm. 7, 12269 (2016).</li><li>Jeon, H. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simple+Chemical+Solution+Deposition+of+Co&#8323;O&#8324;+Thin+Film+Electrocatalyst+for+Oxygen+Evolution+Reaction.">Simple Chemical Solution Deposition of Co&#8323;O&#8324; Thin Film Electrocatalyst for Oxygen Evolution Reaction.</a> ACS Appl Mater Interfaces. 7 (44), 24550-24555 (2015).</li><li>Xia, F., Pring, A., Brugger, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+the+mechanism+and+kinetics+of+pentlandite+oxidation+in+extractive+pyrometallurgy+of+nickel.">Understanding the mechanism and kinetics of pentlandite oxidation in extractive pyrometallurgy of nickel.</a> Mine Eng. 27-28, 11-19 (2012).</li><li>Drebushchak, V. A., Kravchenko, T. A., Pavlyuchenko, V. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+pure+pentlandite+in+bulk.">Synthesis of pure pentlandite in bulk.</a> J Crystal Growth. 193 (4), 728-731 (1998).</li><li>Knop, O., Huang, C. -. H., Reid, K., Carlow, J. S., Woodhams, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chalkogenides+of+the+transition+elements.+X.+X-ray,+neutron,+M&#246;ssbauer,+and+magnetic+studies+of+pentlandite+and+the+&#960;+phases+&#960;(Fe,+Co,+Ni,+S),+Co8MS8,+and+Fe4Ni4MS8+(M+=+Ru,+Rh,+Pd).">Chalkogenides of the transition elements. X. X-ray, neutron, M&#246;ssbauer, and magnetic studies of pentlandite and the &#960; phases &#960;(Fe, Co, Ni, S), Co8MS8, and Fe4Ni4MS8 (M = Ru, Rh, Pd).</a> J Solid State Chem. 16 (1-2), 97-116 (1976).</li><li>Kullerud, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermal+stability+of+pentlandite.">Thermal stability of pentlandite.</a> The Canadian Mineralogist. 7 (3), 353-366 (1963).</li><li>Siracusano, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+electrochemical+study+of+a+PEM+stack+for+water+electrolysis.">An electrochemical study of a PEM stack for water electrolysis.</a> Int J Hydrogen Energy. 37 (2), 1939-1946 (2012).</li></ol>

The authors have nothing to disclose.

The synthesis of Fe4.5Ni4.5S8 was performed in a vacuum-sealed ampule to prevent oxidation of the material during synthesis. During the synthesis, temperature control is the key to obtain a pure product. The first, very slow heating step thereby prevents superheating of the sulfur, which might cause cracking of the ampule due to high sulfur pressure. Even more crucial is the prevention of phase impurities like mono-sulfide solid solutions (mss) by slow heating of the sample. The subsequen...

The storage of fluctuating renewable energy sources such as solar and wind energy is of significant social interest due to the gradual fade of fossil fuels and subsequent need of alternative energy sources. In this respect, hydrogen is a promising sustainable candidate for a molecular energy storage solution because of a clean combustion process.1 Additionally hydrogen could be used as fuel or as starting material for more complex fuels, e.g. methanol. The preferred way for a facile synthesis of hydrogen using carbon neutral resources is the electrochemical reduction of water using sustainable energies.
Currently, platinum and its alloys are known to be the most effective electrocatalysts for the hydrogen evolution reaction (HER) showing low over-potential, a fast reaction rate and operation at high current densities.2 However, due to its high price and low natural abundance, alternative non-noble metal catalysts are required. Among the vast amount of alternative non-precious transition metal catalysts,3 especially transition metal dichalcogenides (MX2; M = Metal; X = S, Se) have been shown to possess high HER activity.4,5,6,7 In this respect, we recently presented Fe4.5Ni4.5S8 as a highly durable and active &#39;rock&#39; HER electrocatalyst. This naturally abundant material is stable under acidic conditions and shows a high intrinsic conductivity with a well-defined catalytic active surface.8
While numerous materials with high HER activities have been reported, the electrode preparation is often accompanied with multiple problems, e.g. reproducibility and satisfactory stabilities (&#62;24 h). Additionally, since the intrinsic conductivity of transition metal based catalysts in bulk is usually high, electrode preparation requires nano-structured catalysts to allow for an efficient electron transfer. These catalysts are then converted into a catalyst ink containing binders such as Nafion and the catalyst. Afterwards, the ink is drop-coated on an inert electrode surface (e.g. glassy carbon). Whereas being reasonably stable at low current densities an increased contact resistance and mediocre adhesion of the catalyst on the electrode support is commonly observed at high current densities.9 Hence, the need for more sufficient preparation methods and electrode materials is evident.
This protocol presents a novel preparation procedure for highly durable and cost efficient electrodes using bulk materials. The prerequisite for such an electrode is a low intrinsic materials resistance. Fe4.5Ni4.5S8 fulfills this criterion and can be obtained from the elements via a simple high-temperature synthesis in sealed silica ampules. The obtained material is characterized with respect to its structure, morphology and composition using powder Xray diffractometry (PXRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and energy dispersive Xray spectroscopy (EDX). The synthesized material is processed to afford two types of bulk electrodes, namely &#39;rock&#39; and &#39;pellet&#39; electrodes. The performance of both electrode types is then investigated using standard electrochemical tests and H2 quantification performed via gas chromatography (GC). A comparison of the performance of both types of electrodes in comparison to commonly used drop-coating experiments is presented.

<table><tbody><tr><td>Iron, powder</td><td>Sigma-Aldrich, http://www.sigmaaldrich.com</td><td>12310-500G-R</td><td></td></tr><tr><td>Nickel, powder</td><td>Sigma-Aldrich, http://www.sigmaaldrich.com</td><td>203904-25G</td><td>H: 351-372-317-412;&lt;br/&gt; P: 281-273-308-313-302+352</td></tr><tr><td>Sulfur, powder</td><td>Sigma-Aldrich, http://www.sigmaaldrich.com</td><td>13803-1KG-R</td><td>H: 315</td></tr><tr><td>Silver Epoxy Glue EC 151 L</td><td>Polytec PT, http://www.polytec-pt.de/de/</td><td>161010-1</td><td>-</td></tr><tr><td>Two Component Epoxy Glue Uhu Plus Endfest</td><td>Uhu, http://www.uhu.com</td><td>-</td><td>&amp;nbsp;H: 315-319-317-411;&lt;br/&gt; &amp;nbsp;P: 101-102-261-272-280-302+352-333+313-362-363-305+351+338-337+313</td></tr><tr><td>Sulfuric Acid &gt;95%</td><td>VWR, https://ru.vwr.com</td><td>231-639-5</td><td>H: 290-314;&lt;br/&gt; S: (1/2)-26-30-45</td></tr><tr><td>PTFE Tube</td><td>-</td><td>-</td><td>Prepare 8 cm long peaces</td></tr><tr><td>Iron Sleeves</td><td>-</td><td>-</td><td>Connect to the copper wire</td></tr><tr><td>Copper Wire</td><td>-</td><td>-</td><td>-</td></tr><tr><td>Lapping Film 3&amp;micro;m, 215.9 mm x 279 mm</td><td>3M, http://3mpro.3mdeutschland.de</td><td>60-0700-0232-8</td><td>Polish with a small amount of water</td></tr><tr><td>Lapping Film 1&amp;micro;m, 215.9 mm x 279 mm</td><td>3M, http://3mpro.3mdeutschland.de</td><td>60-0700-0266-6</td><td>Polish with a small amount of water</td></tr><tr><td>Sand Paper 20 &amp;micro;m, SiC</td><td>-</td><td>-</td><td>-</td></tr><tr><td>Sand Paper 14 &amp;micro;m, SiC</td><td>-</td><td>-</td><td>-</td></tr><tr><td>Dremel Model 225</td><td>Dremel, https://www.dremeleurope.com</td><td>2615022565</td><td>Use grinding pulley wheel for cutting&amp;nbsp;</td></tr><tr><td>Hand Made Pellet Press</td><td>Hand Made</td><td>-</td><td>-</td></tr><tr><td>Stirring Plate</td><td>-</td><td>-</td><td>-</td></tr><tr><td>GAMRY Reference 600</td><td>GAMRY Instruments, https://www.gamry.com</td><td>-</td><td>-</td></tr><tr><td>Gero Furnace 30-3,000 &amp;deg;C</td><td>http://www.carbolite-gero.de</td><td>-</td><td>-</td></tr><tr><td>Quartz glass ampule</td><td>Hand Made</td><td>-</td><td>-</td></tr><tr><td>Vacuum pump</td><td>-</td><td>-</td><td>-</td></tr><tr><td>Hydraulic press</td><td>-</td><td>-</td><td>-</td></tr></tbody></table>

simple methods for the preparation of non-noble metal bulk-electrodes for electrocatalytic applications

The rock material pentlandite with the composition Fe4.5Ni4.5S8 was synthesized via high temperature synthesis from the elements. The structure and composition of the material was characterized via powder X-ray diffraction (PXRD), M&#246;ssbauer spectroscopy (MB), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and energy dispersive X-ray spectroscopy (EDX). Two preparation methods of pentlandite bulk electrodes are presented. In the first approach a piece of synthetic pentlandite rock is directly contacted via a wire ferrule. The second approach utilizes pentlandite pellets, pressed from finely ground powder, which is immobilized in a Teflon casing. Both electrodes, whilst being prepared by an additive-free method, reveal high durability during electrocatalytic conversions in comparison to common drop-coating methods. We herein showcase the striking performance of such electrodes to accomplish the hydrogen evolution reaction (HER) and present a standardized method to evaluate the electrocatalytic performance by electrochemical and gas chromatographic methods. Furthermore, we report stability tests via potentiostatic methods at an overpotential of 0.6 V to explore the material limitations of the electrodes during electrolysis under industrial relevant conditions.

The successful synthesis of Fe4.5Ni4.5S8 possessing the Pentlandite structure is confirmed by powder X-ray diffraction experiments due to the prominent (111), (311), (222), (331) and (511) reflections being present (Figure 1a). A proper temperature control during the reaction, however, is the key to obtain phase pure materials. Notably, mono-sulfide solid solutions (mss), a common impurity of pentlandite materials<sup class="x...

Watch this Scientific Journal Video about Simple Methods for the Preparation of Non-noble Metal Bulk-electrodes for Electrocatalytic Applications at JoVE.com

Simple Methods for the Preparation of Non-noble Metal Bulk-electrodes for Electrocatalytic Applications

A facile preparation method of electrodes using the bulk material Fe4.5Ni4.5S8 is presented. This method provides an alternative technique to conventional electrode fabrication and describes prerequisites for unconventional electrode materials including a straightforward electrocatalytic testing method.

The rock material pentlandite with the composition Fe4.5Ni4.5S8 was synthesized via high temperature synthesis from the elements. The structure and ...

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11.4K Views.  Ruhr-University Bochum. A facile preparation method of electrodes using the bulk material Fe4.5Ni4.5S8 is presented. This method provides an alternative technique to conventional electrode fabrication and describes prerequisites for unconventional electrode materials including a straightforward electrocatalytic testing method.

Video: Simple Methods for the Preparation of Non-noble Metal Bulk-electrodes for Electrocatalytic Applications

On the Preparation and Testing of Fuel Cell Catalysts Using the Thin Film Rotating Disk Electrode Method

We present a step-by-step tutorial to prepare proton exchange membrane fuel cell (PEMFC) catalysts, consisting of Pt nanoparticles (NPs) supported on a high surface area carbon, and to test their performance in thin film rotating disk electrode (TF-RDE) measurements. The TF-RDE methodology is widely used for catalyst screening; nevertheless, the measured performance sometimes considerably differs among research groups. These uncertainties impede the advancement of new catalyst materials and, consequently, several authors discussed possible best practice methods and the importance of benchmarking.
The visual tutorial highlights possible pitfalls in the TF-RDE testing of Pt/C catalysts. A synthesis and testing protocol to assess standard Pt/C catalysts is introduced that can be used together with polycrystalline Pt disks as benchmark catalysts. In particular, this study highlights how the properties of the catalyst film on the glassy carbon (GC) electrode influence the measured performance in TF-RDE testing. To obtain thin, homogeneous catalyst films, not only the catalyst preparation, but also the ink deposition and drying procedures are essential. It is demonstrated that an adjustment of the ink&#39;s pH might be necessary, and how simple control measurements can be used to check film quality. Once reproducible TF-RDE measurements are obtained, determining the Pt loading on the catalyst support (expressed as Pt wt%) and the electrochemical surface area is necessary to normalize the determined reaction rates to either surface area or Pt mass. For the surface area determination, so-called CO stripping, or the determination of the hydrogen underpotential deposition (Hupd) charge, are standard. For the determination of the Pt loading, a straightforward and cheap procedure using digestion in aqua regia with subsequent conversion of Pt(IV) to Pt(II) and UV-vis measurements is introduced.

Preparing and testing Pt/C fuel cell catalysts is subject to continuous discussion in the scientific community with respect to reproducibility and best practice. With the presented work, we intend to present a step-by-step tutorial to make and test Pt/C catalysts, which can serve as benchmark for novel catalyst systems.

We present a step-by-step tutorial to prepare proton exchange membrane fuel cell (PEMFC) catalysts, consisting of Pt nanoparticles (NPs) supported on a ...

Environment

Self-standing Electrochemical Set-up to Enrich Anode-respiring Bacteria On-site

Anaerobic respiration coupled with electron transport to insoluble minerals (referred to as extracellular electron transport [EET]) is thought to be critical for microbial energy production and persistence in many subsurface environments, especially those lacking soluble terminal electron acceptors. While EET-capable microbes have been successfully isolated from various environments, the diversity of bacteria capable of EET is still poorly understood, especially in difficult-to-sample, low energy or extreme environments, such as many subsurface ecosystems. Here, we describe an on-site electrochemical system to enrich EET-capable bacteria using an anode as a respiratory terminal electron acceptor. This anode is connected&#160;to a cathode capable of&#160;catalyzing abiotic oxygen reduction. Comparing this approach with electrocultivation methods that use a potentiostat for poising the electrode potential, the two-electrode system does not require an external power source. We present an example of our on-site enrichment utilized in an alkaline pond at the Cedars, a terrestrial serpentinization site in Northern California. Prior attempts to cultivate mineral reducing bacteria were unsuccessful, which is likely due to the low-biomass nature of this site and/or the low relative abundance of metal reducing microbes. Prior to implementing our two-electrode enrichment, we measured the vertical profile of dissolved oxygen concentration. This allowed us to place the carbon felt anode and platinum-electroplated carbon felt cathode at depths that would support anaerobic and aerobic processes, respectively. Following on-site incubation, we further enriched the anodic electrode in the laboratory and confirmed&#160;a distinct microbial community compared to the surface-attached or biofilm communities normally observed at the Cedars. This enrichment subsequently led to the isolation of the first electrogenic microbe from the Cedars. This method of on-site microbial enrichment has the potential to greatly enhance the isolation of EET-capable bacteria from low biomass or difficult to sample habitats.

On-site microbial enrichment or in situ cultivation techniques can facilitate the isolation of difficult-to-culture microbial taxa, especially from low-biomass or geochemically extreme environments. Here, we describe an electrochemical set-up without using an external power source to enrich microbial strains that are capable of extracellular electron transport (EET).

Anaerobic respiration coupled with electron transport to insoluble minerals (referred to as extracellular electron transport [EET]) is thought to be ...

Synthesis of Platinum-nickel Nanowires and Optimization for Oxygen Reduction Performance

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen reduction reaction. Spontaneous galvanic displacement was used to deposit Pt layers onto Ni nanowire substrates. The synthesis approach produced catalysts with high specific activities and high Pt surface areas. Hydrogen annealing improved Pt and Ni mixing and specific activity. Acid leaching was used to preferentially remove Ni near the nanowire surface, and oxygen annealing was used to stabilize near-surface Ni, improving durability and minimizing Ni dissolution. These protocols detail the optimization of each post-synthesis processing step, including hydrogen annealing to 250 &#176;C, exposure to 0.1 M nitric acid, and oxygen annealing to 175 &#176;C. Through these steps, Pt-Ni nanowires produced increased activities more than an order of magnitude than Pt nanoparticles, while offering significant durability improvements. The presented protocols are based on Pt-Ni systems in the development of fuel cell catalysts. These techniques have also been used for a variety of metal combinations, and can be applied to develop catalysts for a number of electrochemical processes.

&#160; The protocol describes the synthesis and electrochemical testing of platinum-nickel nanowires. Nanowires were synthesized by the galvanic displacement of a nickel nanowire template. Post-synthesis processing, including hydrogen annealing, acid leaching, and oxygen annealing were used to optimize nanowire performance and durability in the oxygen reduction reaction.

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen ...

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity in aqueous CO2 reduction. Different from traditional metal nanocrystals, the synthesis of metal single atoms involves a matrix material that can confine those single atoms and prevent them from aggregation. We report an electrospinning and thermal annealing method to prepare Ni single atoms dispersed and coordinated in a graphene shell, as active centers for CO2 reduction to CO. During the synthesis, N dopants play a critical role in generating graphene vacancies to trap Ni atoms. Aberration-corrected scanning transmission electron microscopy and three-dimensional atom probe tomography were employed to identify the single Ni atomic sites in graphene vacancies. Detailed setup of electrochemical CO2 reduction apparatus coupled with an on-line gas chromatography is also demonstrated. Compared to metallic Ni, Ni single atom catalyst exhibit dramatically improved CO2 reduction and suppressed H2 evolution side reaction.

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

Here, we present a protocol for the synthesis and electrochemical testing of transition metal single atoms coordinated in graphene vacancies as active centers for selective carbon dioxide reduction to carbon monoxide in aqueous solutions.

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity ...

A Rapid Synthesis Method for Au, Pd, and Pt Aerogels Via Direct Solution-Based Reduction

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various precursor noble metal ions with reducing agents in a 1:1 (v/v) ratio results in the formation of metal gels within seconds to minutes compared to much longer synthesis times for other techniques such as sol-gel. Conducting the reduction step in a microcentrifuge tube or small volume conical tube facilitates a proposed nucleation, growth, densification, fusion, equilibration model for gel formation, with final gel geometry smaller than the initial reaction volume. This method takes advantage of the vigorous hydrogen gas evolution as a by-product of the reduction step, and as a consequence of reagent concentrations. The solvent accessible specific surface area is determined with both electrochemical impedance spectroscopy and cyclic voltammetry. After rinsing and freeze drying, the resulting aerogel structure is examined with scanning electron microscopy, X-ray diffractometry, and nitrogen gas adsorption. The synthesis method and characterization techniques result in a close correspondence of aerogel ligament sizes. This synthesis method for noble metal aerogels demonstrates that high specific surface area monoliths may be achieved with a rapid and direct reduction approach.

A rapid, direct solution-based reduction synthesis method to obtain Au, Pd, and Pt aerogels is presented.

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various ...

Three-electrode Coin Cell Preparation and Electrodeposition Analytics for Lithium-ion Batteries

As lithium-ion batteries find use in high energy and power applications, such as in electric and hybrid-electric vehicles, monitoring the degradation and subsequent safety issues becomes increasingly important. In a Li-ion cell setup, the voltage measurement across the positive and negative terminals inherently includes the effect of the cathode and anode which are coupled and sum to the total cell performance. Accordingly, the ability to monitor the degradation aspects associated with a specific electrode is extremely difficult because the electrodes are fundamentally coupled. A three-electrode setup can overcome this problem. By introducing a third (reference) electrode, the influence of each electrode can be decoupled, and the electrochemical properties can be measured independently. The reference electrode (RE) must have a stable potential that can then be calibrated against a known reference, for example, lithium metal. The three-electrode cell can be used to run electrochemical tests such as cycling, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). Three-electrode cell EIS measurements can elucidate the contribution of individual electrode impedance to the full cell. In addition, monitoring the anode potential allows the detection of electrodeposition due to lithium plating, which can cause safety concerns. This is especially important for the fast charging of Li-ion batteries in electric vehicles. In order to monitor and characterize the safety and degradation aspects of an electrochemical cell, a three-electrode setup can prove invaluable. This paper aims to provide a guide to constructing a three-electrode coin cell setup using the 2032-coin cell architecture, which is easy to produce, reliable, and cost-effective.

Three-electrode cells are useful in studying the electrochemistry of lithium-ion batteries. Such an electrochemical setup allows the phenomena associated with the cathode and anode to be decoupled and examined independently. Here, we present a guide for construction and use of a three-electrode coin cell with emphasis on lithium plating analytics.

As lithium-ion batteries find use in high energy and power applications, such as in electric and hybrid-electric vehicles, monitoring the degradation and ...

Engineering

A Continuous-flow Photocatalytic Reactor for the Precisely Controlled Deposition of Metallic Nanoparticles

In this work, a novel photocatalytic reactor for the pulsed and controlled excitation of the photocatalyst and the precise deposition of metallic nanoparticles is developed. Guidelines for the replication of the reactor and its operation are provided in detail. Three different composite systems (Pt/graphene, Pt/TiO2, and Au/TiO2) with monodisperse and uniformly distributed particles are produced by this reactor, and the photodeposition mechanism, as well as the synthesis optimization strategy, are discussed. The synthesis methods and their technical aspects are described comprehensively. The role of the ultraviolet (UV) dose (in each excitation pulse) on the photodeposition process is investigated and the optimum values for each composite system are provided.

For a continuous and scalable synthesis of noble-metal-based nanocomposites, a novel photocatalytic reactor is developed and its structure, operation principles, and product quality optimization strategies are described.

In this work, a novel photocatalytic reactor for the pulsed and controlled excitation of the photocatalyst and the precise deposition of metallic ...

Electrochemical Roughening of Thin-Film Platinum Macro and Microelectrodes

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries of the metal. Using this method, a crack free, thin-film macroelectrode surface with up to 40 times increase in active surface area was obtained. The roughening is easy to do in a standard electrochemical characterization laboratory and incudes the application of voltage pulses followed by extended application of a reductive voltage in a perchloric acid solution. The protocol includes the chemical and electrochemical preparation of both a macroscale (1.2 mm diameter) and microscale (20 &#181;m diameter) platinum disc electrode surface, roughening the electrode surface and characterizing the effects of surface roughening on electrode active surface area. This electrochemical characterization includes cyclic voltammetry and impedance spectroscopy and is demonstrated for both the macroelectrodes and the microelectrodes. Roughening increases electrode active surface area, decreases electrode impedance, increases platinum charge injection limits to those of titanium nitride electrodes of same geometry and improves substrates for adhesion of electrochemically deposited films.

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries. The electrochemical techniques of cyclic voltammetry and impedance spectroscopy are demonstrated to characterize these electrode surfaces.

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries ...

Electrochemical Preparation of Poly(3,4-Ethylenedioxythiophene) Layers on Gold Microelectrodes for Uric Acid-Sensing Applications

Two different methods for the synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) on gold electrodes are described, using electropolymerization of 3,4-ethylenedioxythiophene (EDOT) monomer in an aqueous and an organic solution. Cyclic voltammetry (CV) was used in the synthesis of PEDOT thin layers. Lithium perchlorate (LiClO4) was used as a dopant in both aqueous (aqueous/acetonitrile (ACN)) and organic (propylene carbonate (PC)) solvent systems. After the PEDOT layer was created in the organic system, the electrode surface was acclimatized by successive cycling in an aqueous solution for use as a sensor for aqueous samples. 
The use of an aqueous-based electropolymerization method has the potential benefit of removing the acclimatization step to have a shorter sensor preparation time. Although the aqueous method is more economical and environmentally friendly than the organic solvent method, superior PEDOT formation is obtained in the organic solution. The resulting PEDOT electrode surfaces were characterized by scanning electron microscopy (SEM), which showed the constant growth of PEDOT during electropolymerization from the organic PC solution, with rapid fractal-type growth on gold (Au) microelectrodes.

Electrochemical Preparation of Poly3,4-Ethylenedioxythiophene Layers on Gold Microelectrodes for Uric Acid-Sensing Applications

We describe aqueous and organic solvent systems for the electropolymerization of poly(3,4-ethylenedioxythiophene) to create thin layers on the surface of gold microelectrodes, which are used for sensing low molecular weight analytes.

Two different methods for the synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) on gold electrodes are described, using electropolymerization of ...

Precise Electrochemical Sizing of Individual Electro-Inactive Particles

Nanoimpact electrochemistry enables the time-resolved in situ characterization (e.g., size, catalytic activity) of single nanomaterial units, providing a means of elucidating heterogeneities that would be masked in ensemble studies. To implement this technique with redox inactive particles, a solution-phase redox reaction is used to produce a steady-state background current on a disk ultramicroelectrode. When a particle adsorbs onto the electrode, it produces a stepwise reduction in the exposed electrode area, which produces, in turn, a stepwise decrease in the current commensurate with the size of the adsorbing species. Historically, however, nanoimpact electrochemistry has suffered from &#34;edge effects,&#34; in which the radial diffusion layer formed at the circumference of the ultramicroelectrodes renders the step size dependent not only on the size of the particle but also on where it lands on the electrode. The introduction of electrocatalytic current generation, however, mitigates the heterogeneity caused by edge effects, thus improving the measurement precision. In this approach, termed &#34;electrocatalytic interruption,&#34; a substrate that regenerates the redox probe at the diffusion layer is introduced. This shifts the rate-limiting step of the current generation from diffusion to the homogeneous reaction rate constant, thus reducing flux heterogeneity and increasing the precision of particle sizing by an order of magnitude. The protocol described here explains the set-up and data collection employed in nanoimpact experiments implementing this effect for improved precision in the sizing of redox in-active materials.

As an analytical technique, nanoimpact electrochemistry, an increasingly important approach to counting and characterizing nanometer-scale, electro-inactive particles, suffers from poor precision due to the heterogeneous current distributions that arise from its use of ultramicroelectrodes. Outlined here is a generalized approach, termed "electrocatalytic interruption," that enhances precision in such measurements.

Nanoimpact electrochemistry enables the time-resolved in situ characterization (e.g., size, catalytic activity) of single nanomaterial units, providing a ...