Centimeter-Scale Porous Ta3N5 Single Crystal Monolith Enhances Photoelectrochemical Performance

Semiconductor materials play an important role in converting solar energy to electrical chemical energy as a photoanode to realize photoelectrochemical conversion. Tantalum nitride (Ta3N5) as a semiconductor with a suitable band gap and appropriate band energy positions is considered to be one of the best photoelectrochemical materials. However, poor charge-carrier separation efficiency and charge-carrier mobility greatly limit its wide application in the photoelectrochemical field. Porous single crystal materials with ordered lattice structural coherence and large surface area are expected to greatly improve photogenerated charge-carrier separation efficiency through decreasing electron/hole recombination centers. In this paper, we use a two-step method to grow a porous tantalum nitride single crystal: first removing K atoms from KTaO3 to form TaON, and second removing O atoms from TaON to form (023) facet engineered Ta3N5. In the neutral solution (0.5 M Na2SO4), the onset potential of the photocurrent is lower than 0.2 V-RHE, which is much less than the reported onset potentials (more than 0.4 V-RHE). In addition, the applied bias photon-to-current efficiencies (ABPEs) of (023) facet engineered Ta3N5 can reach about 40% under 400 nm light irradiation, similar to 16 times more than that of the reported Ta3N5 at the same experimental conditions. After 10 h of intensive light irradiation, we show that the porous Ta3N5 single crystal still has a relatively good photoelectrochemical performance. This inspires a wide application of the porous single crystal in the photoelectrochemical area.