Local magnetic spin mismatch promoting photocatalytic overall water splitting with exceptional solar-to-hydrogen efficiency

Abstract

The photocatalytic overall water splitting (POWS) reaction using particulate catalysts is considered as an ideal approach for capturing solar energy and storing it in the form of hydrogen, however, current POWS systems are hindered by the slow separation but fast recombination of the photo-generated charge carriers, hence giving unsatisfactory performances. Here we report a dramatically improved POWS system for a Au-supported Fe₃O₄/N-TiO₂ superparamagnetic photocatalyst promoted by local magnetic field effects. Strong local magnetic flux was induced by a weak external magnetic field of 180 mT, which then resulted in a quantum efficiency of 88.7% at 437 nm at 270 °C without any sacrificial reagent. The mechanism of the magnetic field effects was explored systematically and quantitatively by time-resolved spectroscopic technique and first-principles calculations, which suggested such enhancement was due to the greatly prolonged excitonic lifetime, originating from both the Lorentz force and spin-polarisation effects. By controllable manipulation of both features using local magnetic field, an unprecedented solar-to-hydrogen conversion efficiency of 11.9 ± 0.5% and an overall energy efficiency of 1.16 ± 0.05% were achieved in a particulate POWS system under AM 1.5G simulated solar illumination, which exceeds the STH goal of 10% for practical applications of POWS systems imposed by the United States Department of Energy.