Three-dimensional Cu2O nanorods modified by hydrogen treated Ti3C2TX MXene with enriched oxygen vacancies as a photocathode and a tandem cell for unassisted solar water splitting

Abstract

Cuprous oxide (Cu2O) has been envisioned as a promising photocathode material for photoelectrochemical (PEC) water reduction due to its abundance, scalability and nontoxicity. Herein, a three-dimensional (3D) Cu2O nanorods (NRs) photocathode is prepared by in-situ growing Cu2O NRs on a copper foam substrate. The bare 3D Cu2O NRs photocathode exhibits a high photocurrent density of −4.02 mA cm−2 at 0 V versus the reversible hydrogen electrode (RHE) under AM 1.5 G simulated sunlight. The oxygen vacancies enriched Ti3C2TX flakes are obtained by reducing Ti3C2TX with H2/Ar gas (denoted as H:Ti3C2TX). The H:Ti3C2TX/Cu2O, Ti3C2TX/Cu2O as well as Au/Cu2O composite photocathodes are fabricated through a facile dip-coating method. The H:Ti3C2TX/Cu2O and Ti3C2TX/Cu2O yield a photocurrent density of −5.41 and −4.45 mA cm−2 respectively, which is higher than the bare Cu2O and Au/Cu2O (−4.31 mA cm−2). The results suggest that the Ti3C2TX is more effective than noble metal Au for improving the PEC performance of Cu2O photocathode. The superior performance of H:Ti3C2TX/Cu2O is attributed to enriched oxygen vacancies in the H:Ti3C2TX which can enhance the conductivity, light-harvesting efficiency and charge-transfer ability of fabricated photocathode. A PEC tandem cell with H:Ti3C2TX/Cu2O as the photocathode and BiVO4 as the photoanode is designed for unassisted solar water splitting. Due to the high porosity and optical transmittance of the 3D copper foam substrate, we illuminate the cell from the H:Ti3C2TX/Cu2O side rather than from the BiVO4 side in usual fashion. The present configuration exhibits a 1.6 times higher solar-to-hydrogen (STH) conversion efficiency of 0.55% than the conventional design with a STH conversion efficiency of 0.34%. The enhanced STH conversion efficiency in our configuration is due to the higher light-harvesting efficiency.