A novel carbon black graphite hybrid air-cathode for efficient hydrogen peroxide production in bioelectrochemical systems

•A hybrid air-cathode with the optimal carbon black/graphite ratio of 1:5 is made.•The maximum H2O2 yield is 11.9 mg L−1 h−1 cm−2.•Continuous flow without H2O2 accumulation increases current efficiency.•Oxygen for H2O2 synthesis is mainly contributed by air diffusion (66–94%).•The use of bioanode increases H2O2 yield and current efficiency.

Carbon black and graphite hybrid air-cathode is proved to be effective for H2O2 production in bioelectrochemical systems. The optimal mass ratio of carbon black to graphite is 1:5 with the highest H2O2 yield of 11.9 mg L−1 h−1 cm−2 (12.3 mA cm−2). Continuous flow is found to improve the current efficiency due to the avoidance of H2O2 accumulation. In the biological system, the highest H2O2 yield reaches 3.29 mg L−1h−1 (0.079 kg m−3day−1) with a current efficiency of 72%, which is higher than the abiotic system at the same current density. H2O2 produced in this system is mainly from the oxygen diffused through this air-cathode (>66%), especially when a more negative cathode potential is applied (94% at −1.0 V). This hybrid air-cathode has advantages of high H2O2 yield, high current density and no need of aeration, which make the synthesis of H2O2 more efficient and economical.

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