Unbiased solar H₂ production with current density up to 23 mA cm^-2 by Swiss-cheese black Si coupled with wastewater bioanode

Unbiased photoelectrochemical hydrogen production with high efficiency and durability is highly desired for solar energy storage. Here, we report a microbial photoelectrochemical (MPEC) system that demonstrated superior performance when equipped with bioanodes and black silicon photocathode with a unique "Swiss-cheese" interface. The MPEC utilizes the chemical energy embedded in wastewater organics to boost solar H₂ production, which overcomes barriers on anode H₂O oxidation. Without any bias, the MPEC generates a record photocurrent (up to 23 mA cm^-2) and retains prolonged stability for over 90 hours with high Faradaic efficiency (96-99%). The calculated turnover number for MoS_x catalyst during a 90 h period is 495471 with an average frequency of 1.53 s^-1. The system replaced pure water on the anode with actual wastewater and achieved waste organic removal up to 16 kg COD m^-2 photocathode per day. Cost credits from concurrent wastewater treatment and low-cost design make photoelectrochemical H₂ production practical for the first time.