A Janus cobalt-based catalytic material for electro-splitting of water

Abstract

The future of energy supply depends on innovative breakthroughs regarding the design of cheap, sustainable and efficient systems for the conversion and storage of renewable energy sources. The production of hydrogen through water splitting seems a promising and appealing solution. We found that a robust nanoparticulate electrocatalytic material, H(2)-CoCat, can be electrochemically prepared from cobalt salts in a phosphate buffer. This material consists of metallic cobalt coated with a cobalt-oxo/hydroxo-phosphate layer in contact with the electrolyte and mediates H(2) evolution from neutral aqueous buffer at modest overpotentials. Remarkably, it can be converted on anodic equilibration into the previously described amorphous cobalt oxide film (O(2)-CoCat or CoPi) catalysing O(2) evolution. The switch between the two catalytic forms is fully reversible and corresponds to a local interconversion between two morphologies and compositions at the surface of the electrode. After deposition, the noble-metal-free coating thus functions as a robust, bifunctional and switchable catalyst.

Bi‐Functional Iron‐Only Electrodes for Efficient Water Splitting with Enhanced Stability through In Situ Electrochemical Regeneration

“…CoCat showed HER activity of −2 mA cm −2 at η = 385 mV and OER activity of +1 mA cm −2 at η = 545 mV. [ 47 ] NiCat showed HER activity of −1.52 mA cm −2 at η = 452 mV and OER activity of +0.6 mA cm −2 at η = 618 mV. [ 48 ] In these materials, the potential controlled transformation between different catalytic species and morphologies was shown to be responsible for the bi-functional activity.…”

“…H 2 -CoCat is reported to contain metallic cobalt active sites in an oxo-hydroxy-phosphate matrix, whereas O 2 -CoCat, more widely known as CoP i is a cobalt oxide. [ 27,47 ] The analogous NiCat is similar replacing cobalt and phosphate with nickel and borate. [ 48 ] Unlike these materials, however, here the two catalytic phases are not likely to exchange through solution via a dissolution-deposition mechanism, but instead may convert in the solid state.…”

One‐Dimensional Earth‐Abundant Nanomaterials for Water‐Splitting Electrocatalysts

“…One of the earliest demonstrations of the non‐noble‐metal bifunctional HER/OER electrocatalysts, although not in 1D morphologies, was reported by the Artero group in 2012 88. In their work, a nanoparticulate material, namely H 2 ‐CoCat, was electrochemically synthesized from cobalt salts in a phosphate buffer solution.…”

Mo2C nanoparticles embedded within bacterial cellulose-derived 3D N-doped carbon nanofiber networks for efficient hydrogen evolution

“…For instance, Mo 2 C@N-CNFs require an overpotential of 437 mV to produce a current density of 10 mA cm − 2 at pH 7 (Supplementary Figure S15c). Nevertheless, the HER activity in neutral media is better than that of Mo 2 C embedded N-doped carbon nanotubes, 17 cobaltembedded nitrogen-rich carbon nanotubes 41 and metallic cobalt@co-balt-oxo/hydroxo phosphate, 42 among others. The Tafel slope at pH 7 is 76.7 mV dec − 1 , which is similar to that of high-quality Pt/C catalyst (58.1 mV dec − 1 ) (Supplementary Figure S15d).…”