Enhancing the Hydrogen Evolution Reaction with Alloy-TiO2 Composites

Abstract

Titania particles embedded into metals that are known hydrogen evolution reaction (HER) electrocatalysts have been shown to further accelerate HER in a number of different systems. In the case of electrodeposited Ni-W-TiO2, the improved HER was attributed to surface roughening,1 in a report of Ni-P-TiO2 nonstoichiometric oxides were responsible for facilitating H reduction/adsorption,2 sol-gel prepared Ni-TiO2 and Ni-Co-TiO2 with and without carbon nanotubes also showed enhanced HER thought to be due to a hypo–hyper d-electronic configuration effect,3 and reports of an electrodeposited Ni-Mo-TiO2 composite attributed HER enhancement with titania to changes in Ni-Mo composition, porosity and surface roughening.4 In order to better understand this phenomenon, two different alloy systems, Ni-W and Co-Mo, were electrodeposited in an electrolyte containing titania to fabricate the alloy composites. The HER behavior was characterized with and without TiO2 in an alkaline electrolyte. Alloys and composites with low amounts of TiO2 ~ 1-5 wt % were galvanostatically deposited onto copper rotating cylinder electrodes. The HER behavior was also characterized with the working electrode rotated to ensure the elimination of mass transport effects. The compositional target of the alloys were those with comparable amounts of W (in Ni-W) and Mo (in Co-Mo) to achieve favorable HER even without TiO2 addition. The presence of the titania particles in the electrodeposition electrolyte influenced both the HER occurring during electrodeposition from a citrate-boric acid electrolyte and the metal partial current densities. HER in a sodium hydroxide electrolyte was indeed enhanced with the TiO2 composites. The composites exhibited a favorable decrease in the HER overpotential, HER Tafel slope and in some cases an increase in the exchange current density when the electroactive area and alloy metal ratio was the same. The results confirm a dominant Volmer-Heyrovsky type of HER mechanism. There is a similarity between both the reduction reactions occurring during the electrodeposition fabrication process and the HER alone in the alkaline electrolyte; in both cases it is hypothesized that TiO2 reduces adsorbed species that facilitates the electrochemical reactions during deposition of the composites and also helps to promote the HER in an alkaline electrolyte. References Y. Zou, Z. Xiao, X. Fei, X. Ren, Materials Protection 37 24–26 (2004).B. Łosiewicz, A. Budniok, A. Lasia, and E. Łągiewka, Polish Journal of Chemistry 78, 1457-1476 (2004).P. Paunović, O. Popovski, A. Dimitrov, D. Slavkov, E. Lefterova, S. H. Jordanov, Electrochimica Acta 52 1810-1817 (2006).A. R. Shetty, A. C. Hegde, Materials Science for Energy Technologies 1, 97-105 (2018).