Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA.
Chem Commun (Camb). 2018 Jun 8;54(47):5943-5955. doi: 10.1039/c8cc01830h.
Renewable energy-driven hydrogen production from electrocatalytic and photocatalytic water splitting has been widely recognized as a promising approach to utilize green energy resources and hence reduces our dependence on legacy fossil fuels as well as alleviates net carbon dioxide emissions. The realization of large-scale water splitting, however, is mainly impeded by its slow kinetics, particularly because of its sluggish anodic half reaction, the oxygen evolution reaction (OER), whose product O2 is ironically not of high value. In fact, the co-production of H2 and O2 in conventional water electrolysis may result in the formation of explosive H2/O2 gas mixtures due to gas crossover and reactive oxygen species (ROS); both pose safety concerns and shorten the lifetimes of water splitting cells. With these considerations in mind, replacing the OER with thermodynamically more favorable organic oxidation reactions is much more preferred, which will not only substantially reduce the voltage input for H2 evolution from water and avoid the generation of H2/O2 gas mixtures and ROS, but also possibly lead to the co-production of value-added organic products on the anode. Indeed, such an innovative strategy for H2 production integrated with valuable organic oxidation has attracted increasing attention in both electrocatalysis and photocatalysis. This feature article showcases the most recent examples along this endeavor. As exemplified in the main text, the oxidative transformation of a variety of organic substrates, including alcohols, ammonia, urea, hydrazine, and biomass-derived intermediate chemicals, can be integrated with energy-efficient H2 evolution. We specifically highlight the importance of oxidative biomass valorization coupled with H2 production, as biomass is the only green carbon source whose scale is comparable to fossil fuels. Finally, the remaining challenges and future opportunities are also discussed.
可再生能源驱动的电催化和光催化水分解制氢已被广泛认为是一种利用绿色能源资源的有前途的方法，从而减少了我们对传统化石燃料的依赖，并缓解了净二氧化碳排放。然而，大规模水分解的实现主要受到其缓慢动力学的阻碍，特别是由于其缓慢的阳极半反应，即析氧反应（OER），其产物 O2 实际上没有高价值。事实上，由于气体交叉和活性氧物质（ROS）的存在，常规水电解中 H2 和 O2 的共生产可能会导致爆炸 H2/O2 气体混合物的形成；这两者都存在安全隐患，并缩短了水分解电池的使用寿命。考虑到这些因素，用热力学上更有利的有机氧化反应代替 OER 更受欢迎，这不仅可以大大降低从水中产生 H2 的电压输入，并避免 H2/O2 气体混合物和 ROS 的产生，而且可能导致在阳极上共生产有价值的有机产品。事实上，这种与有价值的有机氧化相结合的创新制氢策略在电催化和光催化领域都引起了越来越多的关注。本文展示了这方面的最新实例。如正文中所述，各种有机底物的氧化转化，包括醇、氨、尿素、肼和生物质衍生的中间化学品，可以与高效节能的 H2 产生相结合。我们特别强调了氧化生物质增值与 H2 生产相结合的重要性，因为生物质是唯一的绿色碳源，其规模可与化石燃料相媲美。最后，还讨论了剩余的挑战和未来的机遇。
