With greenhouse gases such as methane and carbon dioxide contributing significantly to global climate change, sustainable, carbon-neutral fuels are needed to replace fossil fuels for meeting society’s energy needs. A possible replacement for fossil fuels for energy is hydrogen gas derived from photoelectrochemical (PEC) water-splitting. However, existing materials capable of driving photoelectrochemical water-splitting have several problems not limited to poor light absorption at visible wavelengths that compromise the sunlight, poor charge transport within the material, and/or poor photo-stability in aqueous electrolyte solutions. Therefore, new materials must be developed or efforts must be made to solve the issues of existing materials for PEC water-splitting.

Zinc ferrite (ZnFe₂O₄) is a n-type, narrow bandgap (E_g = 1.9 eV) semiconductor with a sufficiently positive valence band to drive PEC water-splitting as a photoanode. However, ZnFe₂O₄ suffers from multiple issues that lower its performance for PEC water-splitting such as extremely poor conductivity, poor light absorption despite its narrow bandgap due to the bandgap’s indirect nature, and poor surface catalytic activity. This work fundamentally studies ZnFe₂O₄ by quantifying its optical, electrical, and catalytic properties and comparing these properties to other established materials for PEC water-splitting. Based on this study, the critical limiting factors for ZnFe2O4’s implementation as a photoanode for PEC water-splitting will be discussed.