Ascorbic acid-induced structural defect in photocatalytic graphitic carbon nitride to boost H2O2 fuel cell performance

In this study, porous g-C3N4 with structural defects of oxygen atom and cyano group (COCN) prepared by thermal polymerization of directly calcinating the mixture of urea and ascorbic acid, is firstly applied in the H2O2 fuel cell. By employing a nickel mesh coated with COCN as the photoanode and iron phthalocyanine (FeIIPc) mixed with g-C3N4 on carbon paper as the cathode, this COCN-based cell exhibits a maximum power density of 0.298 mW·cm−2 in the water solution including 0.1 M HCl under AM 1.5G solar light at air atmosphere, which has an approximate 5.0 times enhancement compared with that of pristine g–C3N4–based one. The corresponding solar-to-electricity conversion efficiency (SECE) of above cell is estimated to be 0.248%. In addition, the photocatalytically produced H2O2 (chemical energy) is stored in water with the electrodes disconnected under light irradiation for 3 h, and then is directly used as the fuel in an H2O2 fuel cell by connecting the electrodes in the dark, yielding a specific capacitance of 5900 mF·cm−2. After 6 h of cell operation, the retention rate of specific capacitance is still as high as 76.9%. The primary results provide a facile strategy to introduce structural defects in g-C3N4 for boosting H2O2 fuel cell performance. [Display omitted] •Porous g-C3N4 with structural defects (COCN) is applied in the H2O2 fuel cell.•The structural defects in COCN facilitate the photocatalytic H2O2 generation.•The COCN as the photoanode produces 0.036 M H2O2 under light irradiation for 3 h.•The COCN-based cell converts solar energy to H2O2 fuel for generating electricity.•The specific capacitance keeps 76.9% of initial value after 6 h of cell operation.