Local pH Change during CoMo-TiO2 Composite Electrodeposition and Alkaline HER Electrolysis

Abstract

Alloys of Co-Mo and Co-Mo-P are of interest for their ability to enhance the hydrogen evolution reaction (HER)1-2 and adding TiO2 to the alloy surface can further enhance HER.3-5 To better understand the influence of TiO2 particles on the electrodeposition of Co-Mo and Co-Mo-P alloys and the resulting HER kinetics, electrodeposition was conducted on a copper mesh electrode in close proximity to a pH probe to measure the local change of pH. The deposit composition and the HER characterized. There was a significant enhancement in the HER exchange current density when TiO2 particles were present in the alloy, taking into account any changes in the surface area. 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 (Fig 1). 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. In contrast, during electrodeposition there is little change in the pH transient with and without having TiO2 particles in the electrolyte. C. C. McCrory, A. Jung, I.M. Ferrer, S.M. Chatman, J.C. Peters, T.F. Jaramillo, J Am Chem Soc, 137 (13) 4347 (2015).A. C. Thenuwara, L. Dheer, N. H. Attanayake, Q. Yan, U. V. Waghmare, D. R. Strongin, ChemCatChem. 10 4832-4837 (2018).A.R. Shetty, A.C. Hegde, Mater. Sci. Energy Technol. 1 (2) 97 (2018).C. Wang, Hubert K. Bilan, E. J. Podlaha, J. Electrochem. Soc. 166 (10) F661 (2019).C. Wang and E. J. Podlaha, J. Electrochem. Soc. 167 (13) 132502 (2020). Figure 1. Change of pH during HER on a Co-Mo electrodeposit at different HER electrolysis current densities. Figure 1