Photoelectrochemical (PEC) water splitting is emerging as a solid platform that could potentially sustain a carbon-free hydrogen community. Among the different semiconducting materials that could integrate a PEC device for overall water splitting, the family of iron-based metal oxides is drawing increasing attention as photoanode materials owing to their earth abundance, low cost, low toxicity, and long-term stability. However, serious bottlenecks for the implementation of this class of materials arise from first, the low current density that far below the theoretical maximum value, and second, the energetic delay between the onset potential the flat-band potential. Here we provide an extensive characterization of the semiconductor-liquid junction (SCLJ) of solution-processed nanostructured iron-based metal oxide photoanodes incuduing α-Fe2O3, CuFe2O4, ZnFe2O4, and LaFeO3. By utilizing a complementary set of operando spectroelectrochemistry such as electrochemical impedance spectroscopy (EIS), intensity-modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS), operando ultraviolet-visible/Raman spectroscopy, and transient phocurrent/photovoltage spectroscopy (TPC/TPV), we provided valuable information regarding energetics across the interface, kinetics of charge transfer and recombination, and reaction intermediates and active sites for device optimization. In particular, directed by operando spectroelectrochemistry, we established a new benchamrk performance of LaFeO3 photoanodes by defect manipulation and surface engineering. In addition, we found a sub-nm Al2O3 surface passivation layer by atonmic layer deposition can form Al3+ – Zn2+ Lewis adducts with a ZnFe2O4 photoanode, thus shifts its onset potential around 100 mV. Our results provide a closer look at the SCLJ and build the fundamental understanding for not only improve the onset potential but also further increase the PEC performance.

Operando spectroelectrochemistry and surface engineering on emerging metal oxide photoanodes for solar water oxidation

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.