Coordination Chemistry Engineered Polymeric Carbon Nitride Photoanode with Ultralow Onset Potential for Water Splitting

Construction of an intimate film/substrate interface is of great importance for a photoelectrode to achieve efficient photoelectrochemical performance. Inspired by coordination chemistry, a polymeric carbon nitride (PCN) film is intimately grown on a Ti-coated substrate by an in situ thermal condensation process. The as-prepared PCN photoanode exhibits a record low onset potential (E_onset) of −0.38 V versus the reversible hydrogen electrode (RHE) and a decent photocurrent density of 242 μA cm⁻² at 1.23 V_RHE for water splitting. Detailed characterization confirms that the origin of the ultralow onset potential is mainly attributed to the substantially reduced interfacial resistance between the Ti-coated substrate and the PCN film benefitting from the constructed interfacial sp² N→Ti coordination bonds. For the first time, the ultralow onset potential enables the PCN photoanode to drive water splitting without external bias with a stable photocurrent density of ≈9 μA cm⁻² up to 1 hour.