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

Summary

A facile preparation method of electrodes using the bulk material Fe_4.5Ni_4.5S₈ 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.

Abstract

The rock material pentlandite with the composition Fe_4.5Ni_4.5S₈ was synthesized via high temperature synthesis from the elements. The structure and composition of the material was characterized via powder X-ray diffraction (PXRD), Mössbauer 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.

Introduction

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.

Curr....

Protocol

1. High-temperature Synthesis of Fe _4.5 Ni _4.5 S ₈

NOTE: The herein described procedure for the synthesis of Fe_4.5Ni_4.5S₈ 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.

1. 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).
2. Evacuate the ampule ....

Results

The successful synthesis of Fe_4.5Ni_4.5S₈ 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

Discussion

The synthesis of Fe_4.5Ni_4.5S₈ 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.......

Materials

List of materials used in this article

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