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Nickel / Conducting Polymer Electrocatalysts For Hydrogen Evolution in an Acidic Medium

Hydrogen, the most abundant element on earth, is the cleanest, sustainable, simplest and ideal fuel. Therefore, hydrogen is increasingly considered as the fuel of the future. The electrolysis of water represents the only renewable and fully environmentally friendly process of hydrogen production, without co-generation of a green-house gas, CO_2. Industrial water electrolysis is currently carried out using a liquid alkaline electrolyte. However, the use of solid polymer electrolyte membrane (PEM)– type generators based on the fuel-cell technology to produce hydrogen from demineralized water would offer a number of advantages compared to the classical alkaline process, especially for residential and small scale applications. However, one of the main obstacles associated with the large-scale commercial application of the PEM hydrogen generator is related to high investment costs, mainly due to the use of noble metals (Pt, Ir, Ru) as electroactive catalyst materials for the hydrogen evolution reaction (HER). Therefore, there is a major need to develop new active, efficient, stable, and cheap electrocatalysts for water splitting in the PEM hydrogen generator, which would offer low overpotentials for the HER at high current densities. We have investigated a possibility of using conducting polymers, polypyrrole and polyaniline, as a catalyst substrate (matrix) for the development of Ni-based HER catalysts with a possibility of their use in the PEM hydrogen generators. The mechanisms and kinetics of the HER in an acidic medium has been investigated using an electrochemical linear polarization (LP) and impedance spectroscopy technique (EIS), while the morphology and structure of the catalyst has been studied using a scanning electron microscopy (SEM) and X-ray diffraction (XRD) technique. It has been shown that Ni / PANI / GC offers a significantly higher electrocatalytic activity compared to Ni electrodeposited on a Cu substrate (Fig.1). This is due to the higher real-to-geometric surface area ratio (surface roughness) (Fig.2), and also due to the higher intrinsic catalytic activity of the Ni / PANI electrocatalyst. Fig. 1: HER LP curves in 0.5M H_2SO_4 for a Ni catalyst layer on a PANI/GC and Cu substrate. Inset: HER Nyquist plot for the two investigated catalysts recorded at -0.3 V. Fig. 2: SEM images of a Ni electrocatalyst on a (a) Cu substrate, and (b) PANI / GC substrate.

Conducting polymers; Ni-catalyst; HER; Electrochemical methods; EIS; SEM; XRD.

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