The Hole‐Tunneling Heterojunction of Hematite‐Based Photoanodes Accelerates Photosynthetic Reaction

Abstract Single‐atom metal‐insulator‐semiconductor (SMIS) heterojunctions based on Sn‐doped Fe 2 O 3 nanorods (SF NRs) were designed by combining atomic deposition of an Al 2 O 3 overlayer with chemical grafting of a RuO x hole‐collector for efficient CO 2 ‐to‐syngas conversion. The RuO x ‐Al 2 O 3 ‐SF photoanode with a 3.0 nm thick Al 2 O 3 overlayer gave a >5‐fold‐enhanced IPCE value of 52.0 % under 370 nm light irradiation at 1.2 V vs. Ag/AgCl, compared to the bare SF NRs. The dielectric field mediated the charge dynamics at the Al 2 O 3 /SF NRs interface. Accumulation of long‐lived holes on the surface of the SF NRs photoabsorber aids fast tunneling transfer of hot holes to single‐atom RuO x species, accelerating the O 2 ‐evolving reaction kinetics. The maximal CO‐evolution rate of 265.3 mmol g −1 h −1 was achieved by integration of double SIMS‐3 photoanodes with a single‐atom Ni‐doped graphene CO 2 ‐reduction‐catalyst cathode; an overall quantum efficiency of 5.7 % was recorded under 450 nm light irradiation.