Ni-based oxides are among the most active non-noble metal catalysts for the oxygen evolution reaction (OER) in alkaline, and inclusion of certain metal ions such as Fe has been reported to promote OER activity but the role played by the guest metal is not fully understood. In this work, we investigated the effect of mode of inclusion of Fe and Al ions in Ni-oxo/hydroxo films electrodeposited from borate buffers (‘Ni-Bi’) on OER activity in borate and KOH electrolytes in the presence and absence of Fe impurities. NiFe-Bi and NiAl-Bi films of varying thickness were co-electrodeposited at different ratios of Fe:Ni or Al:Ni from mixed metal nitrates, and were interrogated as-deposited and after anodic conditioning. The ions were also co-included after electrodeposition of Ni-Bi by addition to the electrolyte and scanning the potential. Fe co-electrodeposition enhanced OER of as-deposited NiFe-Bi relative to Ni-Bi, but NiFe-Bi films still required anodic conditioning in borate to enhance catalysis. Different processes were indicated to result from anodic conditioning that incorporates Fe from the electrolyte versus from Fe co-deposition. Anodic conditioning caused the Ni(OH)<sub>2</sub>/NiOOH redox peaks of Ni-Bi and NiFe-Bi to shift anodically without affecting reversibility, while Fe co-deposition caused more cathodic and more reversible peaks than Ni-Bi. In addition, OER was not promoted at NiFe-Bi films upon anodic conditioning in KOH electrolyte purified from Fe impurities. Addition of Al to the electrolyte poisoned OER catalysis of Ni-Bi and NiFe-Bi, but Al co-electrodeposition in thin and thick NiAl-Bi films did not similarly poison OER in the presence of Fe impurities in solution. Results thus indicated that the effect of these guest metals on OER at Ni-oxo/hydroxo films, whether promoting or inhibiting, depended on the mode of inclusion, pointing to different bulk versus surface roles. This supports a recent hypothesis we made that the increase in OER activity at Ni-Bi with anodic conditioning is caused by surface site modification with Fe inclusion from the electrolyte rather than its bulk co-inclusion in the film.

Electrochemical investigation of the effect of mode of inclusion of guest metal ions Fe and Al on oxygen evolution catalysis at Ni(OH)<sub>2</sub>/NiOOH films in borate and KOH

256th National Meeting (2018)

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Electrochemical investigation of the effect of mode of inclusion of guest metal ions Fe and Al on oxygen evolution catalysis at Ni(OH)2/NiOOH films in borate and KOH

Electrochemical investigation of the effect of mode of inclusion of guest metal ions Fe and Al on oxygen evolution catalysis at Ni(OH)₂/NiOOH films in borate and KOH