Probing the Local pH during HER on TiO2 Promoted Co-Mo Electrocatalysts

Abstract

The HER catalytic performance of electrodeposited Co-Mo thin film electrocatalysts in base can be improved by incorporating nano-TiO2 particles into the metal matrix.1-2 The HER overpotential was significantly reduced, and the exchange current density was substantially higher compared to its Co-Mo counterpart. The embedded TiO2 particles were found to also affect the partial current density of metal deposits during the electrodeposition process. To further probe the influence of the TiO2 particles on both the HER and the electrodeposition, the local pH was investigated. The Co-Mo and Co-Mo-TiO2 thin films were deposited onto copper mesh electrodes from a sulfate-citrate electrolyte with particles suspended in the electrolyte. The HER activity was evaluated in a 1 M NaOH electrolyte at room temperature. The surface morphology was characterized by SEM, and deposit composition was assessed by XRF and EDS. With an in-house designed, 3D printed experimental setup, the local pH of the cathode was monitored during galvanostatic deposition and HER electrolysis. During the electrodeposition process, the trend of local pH change with and without TiO2 particles are the same, consistent with their similar HER partial current densities. During the HER electrolysis, as the current density increases, the local pH value of Co-Mo without particles increases considerably, while the local pH value of Co-Mo-TiO2 remains unaltered. This result suggest that TiO2 particles can buffer the electrode surface and is an important factor in improving the HER catalytic performance. Wang, C.; Bilan, H. K.; Podlaha, E. J., Electrodeposited Co-Mo-TiO2 Electrocatalysts for the Hydrogen Evolution Reaction. Journal of The Electrochemical Society 2019, 166 (10), F661-F669.Wang, C.; Podlaha, E. J., Communication-Electrodeposited Co-Mo-P-TiO2 Composites Electrocatalysts for the Hydrogen Evolution Reaction. Journal of the Electrochemical Society 2020.