Qisen Jia¹, Yanan Wang¹, Yan Zhao¹, Zhenming Tian¹, Luyao Ren¹, Xuejing Cui¹, Guangbo Liu^1,*, Xin Chen^2,3,*, Wenzhen Li⁴, Luhua Jiang^1,*

¹ Nanomaterials & Electrocatalysis Laboratory, College of Materials Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, PR China

² State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, 610500, China

³ Center for Computational Chemistry and Molecular Simulation, College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu 610500, China

⁴ Department of Chemical & Biological Engineering, Iowa State University, Ames, IA 50011-1098, Unites States.

* Corresponding authors: liugb@qust.edu.cn (G. Liu); chenxin830107@pku.edu.cn (X. Chen); luhuajiang@qust.edu.cn (L. Jiang)

Abstract:

Photoelectrocatalytic (PEC) seawater splitting as a green and sustainable route to harvest hydrogen is attractive yet hampered by low activity of photoanodes and unexpected high selectivity to the corrosive and toxic chlorine. Especially, it is full of challenges to unveil the key factors influencing the selectivity of such complex PEC processes. Herein, by regulating the energy band and surface structure of the anatase TiO₂ nanotube array photoanode via nitrogen-doping, the seawater PEC oxidation shifts from Cl^- oxidation reaction (ClOR) dominant on the TiO₂ photoanode (61.6%) to oxygen evolution reaction (OER) dominant on the N-TiO₂ photoanode (62.9%). Comprehensive investigations including operando photoelectrochemical FTIR and DFT calculations unveil that the asymmetric hydrogen-bonding water at the N-TiO₂ electrode/electrolyte interface enriches under illumination, facilitating proton transfer and moderate adsorption strength of oxygen-intermediates, which lowers the energy barrier for the OER yet elevates the energy barrier for the ClOR, resulting to a promoted selectivity towards the OER. The work sheds light on the underlying mechanism of the PEC water oxidation processes, and highlights the crucial role of interfacial water on the PEC selectivity, which could be regulated by controlling the energy band and the surface structure of semiconductors.

Keywords: photoelectrocatalysis; seawater splitting; selectivity; interfacial water structure; energy band structure