Suppressing hydrogen evolution and eliminating sulfation in lead-carbon batteries via potential-matching g-C3N4@rGO nanosheets

Hydrogen evolution reaction (HER) and sulfation on the negative plate are main problems hindering the operation of lead-carbon batteries under high-rate partial-state-of-charge (HRPSoC). Here, reduced graphene oxide nanosheets modified with graphitic carbon nitride (g-C3N4@rGO) were prepared and used as additives in an attempt to solve the above bottleneck. Galvanostatic charge–discharge (GCD) curves show that immobilization g-C3N4 on rGO surface can extend the lower limit of working potential of rGO from −0.3 to −0.9 V, which better matches the working potential range of Pb/PbSO4 redox pair. Theoretical calculations and correlation analyses show that HER can be linked to electrical double-layer capacitors (EDLCs) through two micro kinetic processes: namely, the desorption process of H+ from additive and the migration process of e− reaching additive surface, and that g-C3N4 modification strategy can suppress the HER on the rGO surface while increasing the capacitance of EDLCs. Meanwhile, potential-matched g-C3N4@rGO (θ = 35.76°) is more hydrophilic than pure rGO (118.20°), so the use of g-C3N4@rGO as a battery additive can eliminate sulfation of the negative plate by promoting electrolyte penetration and increasing capacitance contribution. Therefore, the electrochemical performance of g-C3N4@rGO-modified batteries showed a significant improvement over their counterparts, indicating this work is a good attempt.