Electrodeposited Co-Mo-TiO2 Electrocatalysts for the Hydrogen Evolution Reaction (HER)

Abstract

Co-Mo alloys are well known as excellent electrocatalysts for hydrogen generation.1-3 Presented here, Co-Mo-TiO2 composite thin films were electrodeposited onto copper rotating cylinder electrode substrates from citrate electrolytes, and deposited galvanostatically at room temperature. TiO2 micro-scale particles were suspended in the electrolyte mechanically and captured into the growing alloy thin films. The addition of TiO2 particles to the Co-Mo matrix did change the alloy composition at low applied current densities (e.g., 20 mA/cm2), but not at higher current densities (e.g., 100 mA/cm2). The composite composition was very uniform over a wide range of current densities, and the partial current densities that dictate the composition, were all higher when particles were present compared to the particle free alloy. The HER polarization and Tafel slopes were characterized in 1 M sodium hydroxide, and the surface area was examined in a ferricyanide electrolyte. The HER kinetics in sodium hydroxide were dependent on both the Mo and TiO2 composition. The exchange current density exhibited a volcano-type behavior with the Mo composition in the deposit. At the maximum value of the exchange current density, the addition of TiO2 further increased its value to nearly 1 mA/cm2, approximately 3 times higher than the Co-Mo alloys. The overpotential at -10 mA/cm2, ƞ10, decreased when particles were present in the deposit by 22-55 mV compared to their alloy counterparts. The Tafel slope of all deposits with TiO2 were similar in the range of 70-75 mV/dec. The Tafel slopes of the alloy without TiO2, changed with the applied electrodeposited current density, while the composition was also altered, unlike the composites. Interestingly, adding particles to the electrodeposition electrolyte increased the metal partial current densities, but not HER, and in contrast, with the particles embedded into the deposit the HER in an alkaline electrolyte was considerably enhanced. References C. C. McCrory, S. Jung, I. M. Ferrer, S. M. Chatman, J. C. Peters, T. F. Jaramillo, J. Amer. Chem. Soc. 137, 4347 (2015).P. Żabiński, H. Nemoto, S. Meguro, K. Asami, K. Hashimoto, J. Electrochem. Soc. 150 C717 (2003).Y. Zhang, Q. Shao, S. Long, X. Huang, Nano Energy 45, 448 (2018).