Kong Dan, Han Xiaoyu, Shevlin Stephen A, Windle Christopher, Warner Jamie H, Guo Zheng-Xiao, Tang Junwang
Department of Chemical Engineering, University College London, Torrington Place, London WC1E 7JE, U.K.
Department of Chemistry, University College London, 20 Gordon St., London WC1H 0AJ, U.K.
ACS Appl Energy Mater. 2020 Sep 28;3(9):8960-8968. doi: 10.1021/acsaem.0c01153. Epub 2020 Aug 24.
Solar-driven water splitting is highly desirable for hydrogen fuel production, particularly if water oxidation is effectively sustained in a complete cycle and/or by means of stable and efficient photocatalysts of main group elements, for example, carbon and nitrogen. Despite extensive success on H production on polymer photocatalysts, polymers have met with very limited success for the rate-determining step of the water splitting-water oxidation reaction due to the extremely slow "four-hole" chemistry. Here, the synthesized metal-free oxygenated covalent triazine (OCT) is remarkably active for oxygen production in a wide operation window from UV to visible and even to NIR (up to 800 nm), neatly matching the solar spectrum with an unprecedented external quantum efficiency (even 1% at 600 nm) apart from excellent activity for H production under full arc irradiation, a big step moving toward full solar spectrum water splitting. Experimental results and DFT calculations show that the oxygen incorporation not only narrows the band gap but also causes appropriate band-edge shifts. In the end, a controlled small amount of oxygen in the ionothermal reaction is found to be a promising and facile way of achieving such oxygen incorporation. This discovery is a significant step toward both scientific understanding and practical development of metal-free photocatalysts for cost-effective water oxidation and hydrogen generation over a large spectral window.
太阳能驱动的水分解对于氢气燃料生产非常理想，特别是如果水氧化能在完整循环中有效维持，和/或通过主族元素（如碳和氮）的稳定高效光催化剂来实现。尽管聚合物光催化剂在产氢方面取得了广泛成功，但由于极其缓慢的“四孔”化学过程，聚合物在水分解 - 水氧化反应的速率决定步骤中取得的成功非常有限。在此，合成的无金属氧化共价三嗪（OCT）在从紫外到可见光甚至近红外（高达800 nm）的宽操作窗口中对产氧具有显著活性，与太阳光谱完美匹配，具有前所未有的外量子效率（在600 nm处甚至达到1%），此外在全弧照射下产氢活性也优异，这朝着全太阳光谱水分解迈出了一大步。实验结果和密度泛函理论计算表明，氧的掺入不仅缩小了带隙，还导致了合适的能带边缘移动。最后，发现离子热反应中可控的少量氧是实现这种氧掺入的一种有前景且简便的方法。这一发现对于在大光谱窗口中实现经济高效的水氧化和制氢的无金属光催化剂的科学理解和实际开发而言，是重要的一步。
