Molybdenum doped bilayer photoanode nanotubes for enhanced photoelectrochemical water splitting

Abstract

Conversion of solar energy into hydrogen energy via photoelectrochemical (PEC) water splitting is one of the most promising approaches for generation of clean and sustainable hydrogen energy in order to address the alarming global energy crisis and environmental problems. To achieve superior PEC performance and solar to hydrogen efficiency (STH), identification, synthesis, and development of efficient photoelectrocatalysts with suitable band gap and optoelectronic properties along with high PEC activity and durability is highly imperative. With the aim of improving the performance of our previously reported bilayer photoanode of WO3 and Nb and N co-doped SnO2 nanotubes i.e. WO3-(Sn0.95Nb0.05)O2:N NTs, herein, we report a simple and efficient strategy of molybdenum (Mo) doping into the WO3 lattice to tailor the optoelectronic properties such as band gap, charge transfer resistance, and carrier density, etc. The Mo doped bilayer i.e. (W0.98Mo0.02)O3-(Sn0.95Nb0.05)O2:N revealed a higher light absorption ability with reduced band gap (1.88 eV) in comparison to that of the undoped bilayer (1.94 eV). In addition, Mo incorporation offered improvements in charge carrier density, photocurrent density, with reduction in charge transfer resistance, contributing to a STH (∼3.12%), an applied bias photon-to-current efficiency (ABPE ∼ 8% at 0.4 V), including a carrier density (Nd ∼ 7.26 × 1022 cm−3) superior to that of the undoped bilayer photoanode (STH ∼2%, ABPE ∼ 5.76%, and Nd ∼5.11 × 1022 cm−3, respectively). The substitution of Mo6+ for W6+ in the monoclinic lattice, forming the W–O–Mo bonds altered the band structure, realizing further enchantments in the PEC reaction and charge transfer kinetics. Additionally, doped bilayer photoanode revealed excellent long term PEC stability under illumination, suggesting its robustness for PEC water splitting. The present work herein provides a simple and effective Mo doping approach for generation of high performance photoanodes for PEC water splitting.