The oxygen evolution reaction (OER) is the most likely reaction to supply electrons and protons for future green fuel and chemical formation, and thus many materials have been studied for their suitability as OER (pre)catalysts. However, in‑situ and post‑catalytic studies have shown that the harsh OER conditions alter the electrode materials, causing a reconstruction to mainly transition metal oxyhydroxides in alkaline and near‑neutral electrolyte. As this reconstructed phase is the real catalyst, its atomic structure and physical properties must be precisely known. These properties will be affected by the precatalyst and the reconstruction conditions, like the product of a chemical reaction is affected by the substrate and reaction conditions. For the elucidation of such reconstruction processes, a broad range of spectroscopic (in‑situ) methods combined with new, meaningful precursors are required.

Herein, investigations on the reconstruction of several precatalysts such as phosphites,¹ borophosphates,² selenites,³ silicides,⁴ and elemental metal foams are presented. These reconstructions were analysed by in situ Raman and X‑ray absorption spectroscopy together with state‑of‑the‑art post-mortem characterization techniques. In an effort to connect this data, we propose ideas relating the precatalyst structure with the one of the formed oxyhydroxides. Additionally, we critically debate the question: why should a non-oxyhydroxide phase be used for the OER if it will anyway reconstruct? Moreover, as mentioned, also the reconstruction conditions affect the specific nature of the formed oxyhydroxide. Considering this, we present a case, where from the same precatalyst, catalysts with entirely different structural and electrocatalytic properties were obtained by only changing the electrochemical reconstruction conditions (potential, pH, electrolyte composition...).

References:

1. Menezes, P. W. et al. A structurally versatile nickel phosphite acting as a robust bifunctional electrocatalyst for overall water splitting. Energy Environ. Sci. 11, 0–13 (2018).
2. Menezes, P. W. et al. Helical cobalt borophosphates to master durable overall water-splitting. Energy Environ. Sci. 12, 988–999 (2019).
3. Hausmann, J. N. et al. Understanding the formation of bulk- and surface-active layered (oxy)hydroxides for water oxidation starting from a cobalt selenite precursor. Energy Environ. Sci. 13, 3607–3619 (2020).
4. Hausmann, J. N. et al. Evolving Highly Active Oxidic Iron(III) Phase from Corrosion of Intermetallic Iron Silicide to Master Efficient Electrocatalytic Water Oxidation and Selective Oxygenation of 5‐Hydroxymethylfurfural. Adv. Mater. 33, 2008823 (2021).