A new cobalt-nickel-tungstate electrocatalyst for the hydrogen evolution reaction

Finding alternative energy sources have been of prime interest over the past several decades, in order to supplant the inevitably-dwindling reserves of fossil fuels and meet the growing global demands for energy. Hydrogen (H₂) is considered a leading alternative energy source that is both renewable and leaves zero emissions when used. A promising and environmentally-friendly way of producing H₂ is through the hydrogen evolution reaction (HER), which is the cathodic half of the electrochemical splitting of water. The standard potential for HER is 0.0 V vs RHE, and this reaction has been electrochemically studied in both acidic and alkaline media.

Different solid-state electrocatalysts have been studied extensively for water splitting, but such catalysts are inherently difficult to control, manipulate and study at the atomic level. We aim to develop molecular catalysts that can be fine-tuned relatively easily at the atomic level and studied in detail using methods that are common for such molecular systems, such as NMR spectroscopy and single-crystal X-ray crystallography.

Polyoxometalates (POMs) are attractive HER catalyst candidates, due to their rich redox chemistry, and the fact that they can be fine-tuned by structural modifications. Indeed, many POMs have already been reported to promote the photochemical splitting of water. Herein, we report a cobalt-nickel-tungstate system, prepared by a POM-inspired methodology, that is an efficient electrocatalyst for HER, with an activity that is comparable to the non-precious state-of-the-art catalyst MoS₂. Our new system shows an onset potential of -0.255 V vs RHE, with an overpotential of 255 mV relative to Pt (0.0 V vs RHE), which is currently the best HER catalyst. The new catalyst was characterized using various spectroscopic techniques, e.g., FT-IR, Raman, powder XRD, EDX, and ICP-AES, and was found to be both chemically and electrochemically robust in 0.5M H₂SO₄ (pH 1).