Inverse Opal CuCrO₂ Photocathodes for H₂ Production Using Organic Dyes and a Molecular Ni Catalyst

Dye-sensitized photoelectrochemical (DSPEC) cells are an emerging approach to producing solar fuels. The recent development of delafossite CuCrO₂ as a p-type semiconductor has enabled H₂ generation through the coassembly of catalyst and dye components. Here, we present a CuCrO₂ electrode based on a high-surface-area inverse opal (IO) architecture with benchmark performance in DSPEC H₂ generation. Coimmobilization of a phosphonated diketopyrrolopyrrole (DPP-P) or perylene monoimide (PMI-P) dye with a phosphonated molecular Ni catalyst (NiP) demonstrates the ability of IO-CuCrO₂ to photogenerate H₂. A positive photocurrent onset potential of approximately +0.8 V vs RHE was achieved with these photocathodes. The DPP-P-based photoelectrodes delivered photocurrents of -18 μA cm^-2 and generated 160 ± 24 nmol of H₂ cm^-2, whereas the PMI-P-based photocathodes displayed higher photocurrents of -25 μA cm^-2 and produced 215 ± 10 nmol of H₂ cm^-2 at 0.0 V vs RHE over the course of 2 h under visible light illumination (100 mW cm^-2, AM 1.5G, λ > 420 nm, 25 °C). The high performance of the PMI-constructed system is attributed to the well-suited molecular structure and photophysical properties for p-type sensitization. These precious-metal-free photocathodes highlight the benefits of using bespoke IO-CuCrO₂ electrodes as well as the important role of the molecular dye structure in DSPEC fuel synthesis.