Electrodeposited Co-Based Electrocatalysts for Hydrogen Evolution Reaction in an Alkaline Electrolyte
Cheng Wang and Elizabeth J. Podlaha
Department of Chemical & Biomolecular Engineering, Clarkson University
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. The Co-Mo alloy and composites were prepared from a sulfate-citrate electrolyte with particles suspended in the electrolyte. The surface morphology was characterized by SEM, and deposit composition assessed by XRF and EDS. The electrochemical active surface area was characterized using a ferri/ferrocyanide redox reaction and by inspection of the limiting current. The HER activity was evaluated in a 1 M NaOH electrolyte at room temperature. The overpotential of the electrodeposited films at -10 mA/cm2 followed the order: Co-Mo-P-TiO2 > Pt > Co-Mo-TiO2 > Co-Mo > Co, where the alloys and composites had comparable Co-Mo composition ratio. This improvement of HER performance is considered not merely due to surface roughness but mostly an intrinsic one. Interestingly, with the particles embedded into the deposit, the HER in an alkaline electrolyte was considerably enhanced, while in the electrodeposition process, it increased the metal partial current densities, but not HER. To further probe the influence of the TiO2 particle on both the HER and the electrodeposition of the composite the local pH was investigated. Thin films with and without particles were deposited onto copper mesh electrodes from a sulfate-citrate electrolyte with particles suspended in the electrolyte. With a specially designed 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 rapidly, while the local pH value of Co-Mo-TiO2 remains unaltered. This result suggest that TiO2 particles can buffer the electrode surface, facilitating the Heyrovsky step in a Volmer-Heyrovsky mechanism.
Wednesday, September 15, 2021
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