Bifunctional photo-assisted hybrid Zn-air battery for efficient solar power storage and glycerol upgrading

Photo-assisted Zn-air batteries (PZABs) hold promise for advancing sustainable energy systems. Herein, to address challenges associated with the cathode charging oxygen evolution reaction (OER), a photo-assisted hybrid Zn-air battery (PHZAB) was constructed by employing photoelectrocatalytic glycerol oxidation reaction (GOR), which is thermodynamically favorable as a replacement for OER during the charging process. Based on element doping and cocatalyst loading strategies, the CoFe-LDH/Mo:BiVO₄ photoanode was fabricated. Systematic photoelectrochemical tests demonstrate its excellent performance, with a GOR current density of 4.78 mA·cm⁻² at 1.23 V vs. RHE, 2.6 times that of the BiVO₄, and an applied bias photon-to-current efficiency (ABPE) of 2.21%, 3.7 times that of the BiVO₄. Further analysis proves that these modification strategies enhance bulk carrier density, accelerate surface catalytic reactions, and effectively suppress carrier recombination, thus enhancing the photoelectrochemical (PEC) performance. Benefiting from the excellent performance of the CoFe-LDH/Mo:BiVO₄ photoanode and the novel hybrid device structure design, the PHZAB exhibits a maximum round-trip efficiency of 206% (at 0.5 mA·cm⁻²) and a 68.7% electricity saving ratio under 1 sun illumination. Even at 2 mA·cm⁻², a 156% round-trip efficiency and 64.2% electricity saving ratio were maintained. During the photoassisted-charging process, the optimized CoFe-LDH/Mo:BiVO₄ photoanode yields a high GOR performance of a total production rate of 225 mmol·m⁻²·h⁻¹ and formic acid (FA) production rate of 133 mmol·m⁻²·h⁻¹. This work presents a novel bifunctional system toward the rational design of functional devices and materials for simultaneously converting solar energy into chemical energy and enabling reversible solar power storage for on-demand release.