Progress in catalysis is driven by society's needs. The development of new electrocatalysts to make renewable and clean fuels from abundant and easily accessible resources is among the most challenging and demanding tasks for today's scientists and engineers. The electrochemical splitting of water into hydrogen and oxygen has been known for over 200 years, but in the last decade and motivated by the perspective of solar hydrogen production, new catalysts made of earth-abundant materials have emerged. Here we present an overview of recent developments in the non-noble metal catalysts for electrochemical hydrogen evolution reaction (HER). Emphasis is given to the nanostructuring of industrially relevant hydrotreating catalysts as potential HER electrocatalysts. The new syntheses and nanostructuring approaches might pave the way for future development of highly efficient catalysts for energy conversion.

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Nanostructured hydrotreating catalysts for electrochemical hydrogen evolution

ac Impedance of Faradaic reactions involving electrosorbed intermediates—I. Kinetic theory

The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) constitute the two main processes in electrochemical water splitting to produce high-purity hydrogen and oxygen as alternatives to fossil fuel. Catalysts are crucial to high-efficiency conversion of water to hydrogen and oxygen. Although transition metal nitrides (TMNs) are promising HER and OER catalysts due to the unique electronic structure and high electrical conductivity, single-phase nitrides have inferior activity compared to Pt-group metals because of the unsatisfactory metal–hydrogen (M–H) bonding strength. TMNs-based composites in combination with other metals, carbon materials, and metallic compounds have been demonstrated to possess improved catalytic properties because the modified electronic structure leads to balanced M–H bonding strength, synergistic effects, and improved electrochemical stability. Herein, recent progress pertaining to TMNs is reviewed from the perspective of advanced catalysts for electrochemical water splitting. The challenges and future opportunities confronting TMNs-based catalysts are also discussed.

Recent progress of transition metal nitrides for efficient electrocatalytic water splitting

Single nanocrystalline tungsten carbide (WC) was first synthesized on the tips of vertically aligned carbon nanotubes (VA-CNTs) with a hot filament chemical vapor deposition (HF-CVD) method through the directly reaction of tungsten metal with carbon source. The VA-CNTs with preservation of vertical structure integrity and alignment play an important role to support the nanocrystalline WC growth. With the high crystallinity, small size, and uniform distribution of WC particles on the carbon support, the formed WC–CNTs material exhibited an excellent catalytic activity for hydrogen evolution reaction (HER), giving a η10 (the overpotential for driving a current of 10 mA cm–2) of 145 mV, onset potential of 15 mV, exchange current density@ 300 mV of 117.6 mV and Tafel slope values of 72 mV dec–1 in acid solution, and η10 of 137 mV, onset potential of 16 mV, exchange current density@ 300 mV of 33.1 mV and Tafel slope values of 106 mV dec–1 in alkaline media, respectively. Electrochemical stability test further ...

WC Nanocrystals Grown on Vertically Aligned Carbon Nanotubes: An Efficient and Stable Electrocatalyst for Hydrogen Evolution Reaction

In this communication we demonstrate that tungsten carbide, WC, is a promising electrocatalyst for the hydrogen evolution reaction in pH neutral electrolytes. In a systematic investigation of mixed catalysts containing different fractions of WC, W2C, W and WO2 we show that the performance of the catalyst is proportional to its WC content, whereas W2C, W and WO2 play only a minor role. The relationship between WC content and electrocatalytic activity indicates that hydrogen evolution and oxidation are related to similar surface sites preferentially formed on WC. In contrast to anodic conditions, the cathodic polarization diminishes corrosion processes and thus increases the long term stability.

M.F. Bell

Papers

Tungsten carbide catalysts for hydrogen evolution