Design of experiments guided hydrothermal synthesis of CuFeO2 photocathodes for photoelectrochemical hydrogen evolution

Abstract

The development of photocathodes exhibiting sufficient stability, strong visible light absorption, and the capacity to generate high photovoltages is essential for the success of photoelectrochemical hydrogen production. In this study, we report the synthesis and characterisation of CuFeO₂ photocathodes via a one-step hydrothermal deposition process, guided by Design of Experiments (DoE) methodologies. The synthesis parameters, including hydrothermal temperature, hydrothermal time, annealing temperature, and annealing time, were systematically optimised through a Box-Behnken design. Phase pure CuFeO₂ delafossite was obtained, following optimized hydrothermal synthesis at 110 °C for 1 h and annealing at 650 °C for 1 h. The optimized CuFeO₂ photoelectrodes delivered a photocurrent density of 1.7 mA cm⁻² at 0.4 V vs. RHE under 1 sun illumination in N₂-purged 1 M NaOH. Crucially, H₂ evolution was observed and quantified (faradaic efficiency of 40%). Thus, the proposed approach, integrating a one-step hydrothermal synthesis with statistical optimisation, represents the first validation of PEC H₂ production from CuFeO₂ photocathodes. Still persistent self-reduction under strongly cathodic bias was not inhibited. Overall, this study establishes a pragmatic, statistically guided pathway for enhancing the efficiency of CuFeO₂-based photocathodes, thereby addressing practical limitations typically associated with CuFeO₂ materials.