Cobalt-molybdenum and cobalt-molybdenum-based phosphides are known hydrogen evolution electrocatalysts in alkaline electrolytes.¹ Recently it has been shown that the addition of titania particles to create composite Co-Mo-TiO₂ and Co-Mo-P-TiO₂ enhances the hydrogen evolution reaction (HER).² In order to better understand the role of TiO₂ in the these composites, the local pH change was characterized during both electrodeposition and HER. The composites were electrodeposited onto a copper mesh working electrode in close vicinity to a flat-bottom pH probe. During electrodeposition from a citrate-boric acid electrolyte, there in an initial drop of pH followed by a pH rise with time that was not influenced by the presence of TiO₂. However, there was a significant change in the local pH when TiO₂ was present in Co-Mo-based electrocatalyst during the HER process. Without TiO₂ particles present in the solid state, the local pH change during electrolysis follows an expected increase with time, while with embedded TiO₂ particles in the metal matrix, the local pH initially decreases slightly and remains constant with time. The results suggest that the enhanced HER performance with TiO₂ in the alloy composite electrocatalyst is a consequence of the buffering of the local pH.

References

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