Search

Poly(heptazine imide) (PHI) polymers have been widely studied, owing to their excellent activity as photocatalysts for various reactions. Their photocatalytic activity has been attributed to defects, optical absorption, or synergistic effects with ions in the reaction media. However, the role of the crystal structure of PHI in photocatalytic activity has not been elucidated. Herein, we reveal a direct correlation between the photocatalytic production of hydrogen (H2) and the crystal structure of PHI. We synthesized polymeric carbon nitride materials focusing on different PHI (001)/(002) crystal plane ratios, high specific surface area, and enhanced light response by co-polymerizing organic monomers in a KCl/LiBr molten salt medium. Theoretical and experimental results disclose that the charge carrier dynamics and electron mobility govern the photoactivity of PHI. The best photocatalyst, which had the highest abundance of PHI (100) planes, showed state-of-the-art performance for the hydrogen evolution reaction, with apparent quantum efficiencies of 15.6% at 405 nm and 1.32% at 595 nm, and for the production of H2O2in pure water under visible light (66.7 μmol g–1h–1).

A large amount of carbon dioxide emissions have caused a greenhouse effect and even disrupted the global ecological balance. Therefore, it is urgent and significant to achieve emission reduction of CO2. The use of electrochemistry to reduce carbon dioxide into valuable chemicals and fuels is a sustainable strategy. Here, we present the electrochemical reduction of CO2into CO in a proton-conducting solid oxide electrolyzer at a low temperature. We exsolve the active metal–oxide interfaces NixCu1–x–NbTi0.4Mn0.1O4−δ(NTMO) in a composite cathode by a synergistic doping strategy to increase the length and tailor the composition of the active interfaces and, hence, to promote CO2reduction. By adjustment of the ratio of the nickel–copper alloy at the metal–oxide interface, it is found that the best performance can appear with an applied voltage of 0.8 V under the composition of Ni0.5Cu0.5–NTMO. A remarkable current efficiency of 99.8% is achieved with CO production at 0.71 mL min–1cm–2at a temperature as low as 600 °C. This illustrates the application prospects of electrochemical reduction of CO2in a solid oxide electrolyzer through interface engineering.