Shixu Song, Yan Zhao, Qisen Jia, Wanqing Yu, Teng Fu, Fengfei Li, Jing Liu, Luhua Jiang*

Nanomaterials & Electrocatalysis Laboratory, College of Materials Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, P.R. China

Abstract: The sluggish methanol oxidation kinetics has seriously hindered the development of direct methanol fuel cells. Photo-electro-catalysis is expected to accelerate reaction rates, yet suffers from lack of efficient photoelectrocatalysts and more importantly, less understanding on photo-electro-catalysis mechanism. Herein, a unique CuNb₂O₅ nanorod array with excellent light adsorption and charge transfer ability, on which supports Pt nanoparticles, is constructed for photo-electrocatalytic methanol oxidation reaction (MOR).Systematical investigation discovers a potential-dependent photo-electro-catalysis coupling mechanism, i.e., at lower potential bias where the Fermi level of semiconductor (E_f,s) is beyond the Fermi level of Pt (E_f,Pt), electrons transferring from Pt to semiconductor is switched off, so semiconductor CuNb₂O₅ alone takes a dominant role for both methanol and water activation; at higher potential bias where E_f,s is below E_f,Pt, electrons flowing from Pt to semiconductor is switched on, so methanol dehydrogenation on Pt surface is allowed energetically. Further investigation on the MOR processes prompts us to propose a MOR pathway that methanol dehydrogenates on Pt surface, with the aid of *OH from the photo-activated water on CuNb₂O₅ to proceed via formaldehyde, formic acid to carbon dioxide, resulting to a low apparent activation energy and fast kinetics of MOR as compared to its counterpart Pt/Nb₂O₅. This work not only provides an efficient photoelectrocatalyst for methanol oxidation, but also sheds lights on the underlying photo-electro-catalysis coupling mechanism over semiconductor-metal catalysts.

Keywords: Methanol oxidation; photo-electrocatalysis; coupling mechanism; Nb₂O₅ nanorod array; band structure.

* Corresponding author: luhuajiang@qust.edu.cn (L. Jiang)