Hydrous RuO2 and CoxNy difunction-modified Ta3N5@Ta2N multi-heterojunction nanoplates for efficient visible-light-driven photocatalytic hydrogen production

To overcome the intrinsic drawbacks of Ta3N5 such as charge carrier recombination and serious self-oxidation, constructing difunctional multi-heterojunction is very promising and challenging for local selective modifications. Hydrous RuO2 and CoxNy difuntionally modified Ta3N5@Ta2N multi-heterojunction nanoplates were fabricated by high-temperature nitridation reduction of Co3+-modified Ta2O5@Ta3N5, followed by photooxidation deposition of Ru3+. The structural and compositional features were modulated by optimizing the nitridation time and Ru-modifying amount. Interestingly, synergetic effects of CoxNy/Ta2N/Ta3N5 and RuO2/Ta2N/Ta3N5 on charge carrier separation and transfer, and on decrease in the HER and OER overpotentials about 73 mV and 238 mV, respectively, were observed. Improved visible light absorption was attributed to a localized surface plasmon resonance (LSPR) effect by subnitride Co5.47N, sub-bandgap behavior of Ta2N, and anion defect N-vacancies. Increased charge transfer resistance by CoxNy/Ta2N interface was significantly reduced by further constructing hydrous RuO2/Ta2N heterojunction, where new Ru–O–Ta linkages facilitated fast separation and transfer of charge carriers, and increased surface hydroxyl groups was beneficial to the adsorption of water molecules. Micropores also provided more photoactive sites. All above factors cooperatively enhanced the visible-light photocatalytic H2-evolution activity, which was 1395.35 μmol·g−1·h−1, about 6.53 times higher than that of Ta2O5@Ta3N5. Its apparent quantum efficiency reaches to 5.76% under irradiance intensity of 15 mW cm−2 at 420 nm. Constructing difunctional multi-heterojunction provides a promising avenue to design efficient and stable Ta3N5-based photocatalysts for solar water splitting.