In this work, we propose a regrowth strategy to prepare a photocathode with CuBi₂O₄ coating on Zn-doped CuBi₂O₄, followed by oxygen vacancy modulation to facilitate interfacial hydrogen evolution reactions.

Tunable properties prompt the development of different “tailor-made” functional ionic liquids (FILs) for specific tasks. FILs with an ether group are good solvents for many organic compounds and enzymatic reactions. However, ionic composition influences the solubility by affecting the physiochemical properties of these FILs. To address the structure effect, a series of novel FILs with a mono-ether group (ME) based on imidazole were prepared through cationic functionalization and anionic exchange reactions, and characterized by NMR, mass spectroscopy, and Thermogravimetric analysis (TGA). The effect of ionic composition (cationic structure and anions) on density, viscosity, ionic conductivity, electrochemical window, and thermal properties of these ME-FILs were systematically investigated. In general, the viscosity and heat capacity increases with the bigger cationic volume of ME-FILs; in particular, the 2-alkyl substitution of imidazolium enhances the viscosity remarkably, whereas the density and conductivity decrease on the condition of the same [NTf₂]⁻ anion; For these ME-FILs with the same cations, the density follows the order of [NTf₂]⁻ > [PF₆]⁻ > [BF₄]⁻. The viscosity follows the order of [PF₆]⁻ > [BF₄]⁻ > [NTf₂]⁻. Ion conductivity follows the order of [NTf₂]⁻ ≈ [BF₄]⁻ > [PF₆]⁻. It is noted that the dynamic density has a good linear relationship with the temperature, and the slopes are the same for all ME-FILs. Furthermore, these ME-FILs have broad electrochemical windows and glass transition temperatures in addition to a cold crystallization and a melt temperature for ME-FIL7. Therefore, the cationic structure and counter anion affect the physicochemical properties of these ME-FILs together.

BiVO₄ is a highly promising material for Photoelectrochemical (PEC) water splitting photoanodes due to its narrow band gap value (~2.4 eV) and its ability to efficiently absorb visible light. However, the short hole migration distance, severe surface complexation, and low carrier separation efficiency limit its application. Therefore, in this paper, BiVO₄ was modified by loading CoOOH cocatalyst on the rare earth element Nd-doped BiVO₄ (Nd-BiVO₄) photoanode. The physical characterization and electrochemical test results showed that Nd doping will cause lattice distortion of BiVO₄ and introduce impurity energy levels to capture electrons to increase carrier concentration, thereby improving carrier separation efficiency. Further loading of surface CoOOH cocatalyst can accelerate charge separation and inhibit electron–hole recombination. Ultimately, the prepared target photoanode (CoOOH-Nd-BiVO₄) exhibits an excellent photocurrent density (2.4 mAcm⁻²) at 1.23 V versus reversible hydrogen electrode potential (vs. RHE), which is 2.67 times higher than that of pure BiVO₄ (0.9 mA cm⁻²), and the onset potential is negatively shifted by 214 mV. The formation of the internal energy states of rare earth metal elements can reduce the photoexcited electron–hole pair recombination, so as to achieve efficient photochemical water decomposition ability. CoOOH is an efficient and suitable oxygen evolution cocatalyst (OEC), and OEC decoration of BiVO₄ surface is of great significance for inhibiting surface charge recombination. This work provides a new strategy for achieving effective PEC water oxidation of BiVO₄.