Electrodeposition of cuprous oxide on a porous copper framework for an improved photoelectrochemical performance

Abstract Photoelectrochemical (PEC) water splitting can be an efficient and economically feasible alternative for hydrogen production if easily processed photoelectrodes made of inexpensive and abundant materials are employed. Here, we present the preparation of porous Cu₂O photocathodes with good PEC performance using solely inexpensive electrodeposition methods. Firstly, porous Cu structures with delicate pore networks were deposited on flat Cu substrates employing hydrogen-bubble-assisted Cu deposition. In a second electrodeposition step, the porous Cu structures were mechanically reinforced and subsequently detached from the substrates to obtain free-standing porous frameworks. In a third and final step, photoactive Cu₂O films were electrodeposited. The PEC water splitting performance in 0.5 M Na₂SO₄ (pH ∼6) shows that these photocathodes have photocurrents of up to −2.25 mA cm⁻² at 0 V versus RHE while maintaining a low dark current. In contrast, the Cu₂O deposited on a flat Cu sample showed photocurrents only up to −1.25 mA cm⁻². This performance increase results from the significantly higher reactive surface area while maintaining a thin and homogeneous Cu₂O layer with small grain sizes and therefore higher hole concentrations as determined by Mott-Schottky analysis. The free-standing porous Cu₂O samples show a direct optical transmittance of 23% (λ = 400–800 nm) and can therefore be used in tandem structures with a photoanode in full PEC cells. Graphical abstract