Bifunctional oxygen electrocatalyst derived from photochlorinated graphene for rechargeable solid-state Zn-air...

Photochlorination method was used to engineer the structural defects and covalent CCl bonds in graphene. Cl coverage of 18 atom% was successfully confirmed by X-ray photoelectron spectroscopy, and D, G and 2D peaks changes upon irradiation were monitored by Raman. The mobility of chlorinated graphene field-effect transistor decreased to 66.1 cm²/(V s) in comparison to pristine graphene of 730.4 cm²/(V s). Raman indicated that the defects and CCl bonds are sensitively associated with the irradiation time, thus the structural defects and composition can be engineered accordingly. Given the creation of active sites, namely the polarization of carbon, as well as fast ionic and electronic transport, chlorinated graphene has demanded features for electrocatalytic reactions. As a proof of concept, chlorinated vertically-oriented graphene grown on carbon cloth (CC@VG) served as excellent bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) free-standing electrodes, showing overpotential of 405 mV for OER, Tafel slope of 56 mV, which has better durability than that of commercial Ir/C. Meanwhile, the ORR reduction peak appeared at 0.776 V vs. RHE, more positive than that of carbon cloth (0.60 V). All-solid-state Zn-air battery (ZABs) using chlorinated CC@VG as bifunctional air-cathode showed stable discharge voltage of 1.28 V at current density of 2 mA/cm², power density of 45.8 mW/cm² at 80 mA/cm². More than 108 discharge/charge cycles (20 min per cycle) was obtained at current density of 2 mA/cm², and round-trip efficiency decreased from 57.4% to 50.0%. Present work developed a universal chlorination method to endow carbonaceous materials with abundant defects and polarized carbon as active site as efficient bifunctional electrocatalysts, and opened a new avenue for developing promising air-cathodes for rechargeable solid-state ZABs.