(521az) Local pH Change during Alkaline HER Electrolysis with Electrodeposited Co-Mo-Based Titania Composite Electrocatalysts

Electrodeposited composites of Co-Mo-TiO₂ and Co-Mo-P-TiO₂ are compared to their alloy counterparts to show that the addition of TiO₂ on the electrocatalyst surface can enhance the hydrogen evolution reaction (HER). In order to better understand the role of TiO₂ in these composites, the local pH change was characterized during HER. The composites were electrodeposited onto copper mesh working electrodes in close vicinity to a flat-bottom pH probe; conditions for the deposit were determined from steady state voltammetry experiments and the deposit composition characterized. HER was compared with different electrocatalyst composition in an alkaline NaOH electrolyte reporting overpotential, Tafel slope and the exchange current density. There was a significant enhancement in the HER overpotential and exchange current density when TiO₂ particles were present in the alloy. The enhancement was associated with a local pH change. Without TiO₂ particles present in the solid state, the local pH change follows an expected increase with time as hydrogen is evolved and the hydroxide ion is generated at the electrode surface. In contrast, when TiO₂ particles were present at the surface and in the metal alloy matrix, the local pH initially decreases slightly and remains constant. 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.