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 sp(2) 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.