Effect of Surface‐Adsorbed and Intercalated (Oxy)anions on the Oxygen Evolution Reaction

Abstract

As the kinetically demanding oxygen evolution reaction (OER) is crucial for the decarbonization of our society, a wide range of (pre)catalysts with various non‐active‐site elements (e.g., Mo, S, Se, N, P, C, Si…) have been investigated. Thermodynamics dictate that these elements oxidize during industrial operation. The formed oxyanions are water soluble and thus predominantly leach in a reconstruction process. Nevertheless, recently, it was unveiled that these thermodynamically stable (oxy)anions can adsorb on the surface or intercalate in the interlayer space of the active catalyst. There, they tune the electronic properties of the active sites and can interact with the reaction intermediates, changing the OER kinetics and potentially breaking the persisting OER *OH/*OOH scaling relations. Thus, the addition of (oxy)anions to the electrolyte opens a new design dimension for OER catalysis and the herein discussed observations deepen the understanding of the role of anions in the OER.

Role of Fe–O–M Bond in Controlling the Electroactive Species Generation from the FeMO4 (M: Mo and W) Electro(pre)catalyst during OER

“…{MoO 4 } may be present in α-FeO(OH) through two possible modes, that is, chemical adsorption (with a proper covalent interaction) and physical adsorption (van der Waals or ionic interaction). 70 Whatever the adsorption mode is, the irregular (nearly amorphous)…”

“…Herein, the residual {MoO 4 } units randomly distributed over the reconstructed α-FeO­(OH) catalyst perhaps make the catalyst a heterojunction material which facilitates the charge transport, as evident from the lower R ct value in compared to its ex situ prepared and deposited FeO­(OH) materials. {MoO 4 } may be present in α-FeO­(OH) through two possible modes, that is, chemical adsorption (with a proper covalent interaction) and physical adsorption (van der Waals or ionic interaction) . Whatever the adsorption mode is, the irregular (nearly amorphous) arrangement of {MoO 4 } over the in situ formed FeO­(OH) presumably enhances the surface area as evident from the physically determined ECSA value for the electrochemically modified FeMoO 4 .…”

“…The porous structure also allows free electrolyte diffusion through this newly formed surface. Additionally, the movement of the oxy anions trapped in the surface may help to build a perfect double layer which may not be favorable for other materials tested herein …”

“…The porous structure also allows free electrolyte diffusion through this newly formed surface. Additionally, the movement of the oxy anions trapped in the surface may help to build a perfect double layer which may not be favorable for other materials tested herein 70. In this study, solvothermally prepared FeMoO 4 nanocrystals when deposited on the NF substrate acted as the anode material to deliver promisingly high current density at considerably low overpotential for alkaline OER.…”

Oxygen Evolution Activity of Amorphous Cobalt Oxyhydroxides: Interconnecting Precatalyst Reconstruction, Long Range Order, Buffer-Binding, Morphology, Mass Transport, and Operation Temperature

“…However, little is known on the effect of different buffers on the CoCat phase formed from a precatalyst especially as previously studied systems with various buffers did not fully convert to CoCat. [24,25] Further, it is unknown how far the nature of precursor material determines which kind of CoCat is formed and how structural and morphological changes of CoCat phases influence the OER activity.…”