Abstract Introduction of the photothermal effect into transition‐metal oxide photoanodes has been proven to be an effective method to improve the photoelectrochemical (PEC) water‐splitting performance. However, the precise role of the photothermal effect on the PEC performance of photoanodes is still not well understood. Herein, spinel‐structured ZnFe2O4 nanoparticles are deposited on the surface of hematite (Fe2O3), and the ZnFe2O4/Fe2O3 photoanode achieves a high photocurrent density of 3.17 mA cm−2 at 1.23 V versus a reversible hydrogen electrode (VRHE) due to the photothermal effect of ZnFe2O4. Considering that the hopping of electron small polarons induced by oxygen vacancies is thermally activated, we clarify that the main reason for the enhanced PEC performance via the photothermal effect is the promoted mobility of electron small polarons that are bound to positively charged oxygen vacancies. Under the synergistic effect of oxygen vacancies and the photothermal effect, the electron conductivity and PEC performance are significantly improved, which provide fundamental insights into the impact of the photothermal effect on the PEC performance of small polaron‐type semiconductor photoanodes.
