Untapped Potential of Scrap Brass Alloy—A New Frontier in the Use of Brass-Based Photocathodes for Stable and Durable Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting is a promising way to produce green hydrogen. However, one of the bottlenecks in realizing scalable green hydrogen production systems is the inability to identify and fabricate earth abundant, stable, and durable photocathodes. The main challenges with the reported photocathodes so far are their instability in aqueous solutions and the use of precious unabundant materials. To this end, the use of scrap materials to fabricate highly stable photocathodes would solve the two main challenges. Herein, scrap brass alloys with different zinc contents were used to fabricate photocathodes for photoelectrochemical green hydrogen production. The scrap brass alloy with 5% Zn showed enhancement in the photocurrent density of −0.26 mA cm⁻² at 0.62 V vs. reversible hydrogen electrode (RHE), high long-term stability up to four hours under continuous illumination, high charge carrier density of 6.2 × 10²¹ cm⁻³ and less total resistance than the other brass samples. Through electrochemical impedance spectroscopy (EIS), the presence of surface states was verified. The 95Cu–5Zn sample showed an amount of evolved hydrogen of 0.2658 μmole after one hour of continuous illumination (area = 0.5 cm²), while the 100Cu sample only showed 3.965 nmole after 20 minutes of continuous illumination before being completely reduced to copper. Density functional theory (DFT) calculations were used to study the optical and electronic properties of the best-performing sample. This work is the first to systematically and fundamentally study scrap brass as a promising material for a more stable and durable PEC water splitting.