Department of Chemistry and Biochemistry, Utah State University , Logan, Utah 84322, United States.
Department of Chemistry, University of California , Riverside, California 92521, United States.
J Am Chem Soc. 2017 Sep 6;139(35):12283-12290. doi: 10.1021/jacs.7b06434. Epub 2017 Aug 22.
The development of low-cost hybrid water splitting-biosynthetic systems that mimic natural photosynthesis to achieve solar-to-chemical conversion is of great promise for future energy demands, but often limited by the kinetically sluggish hydrogen evolution reaction (HER) on the surface of nonprecious transition metal catalysts in neutral media. It is thus highly desirable to rationally tailor the reaction interface to boost the neutral HER catalytic kinetics. Herein, we report a general surface nitrogen modification of diverse transition metals (e.g., iron, cobalt, nickel, copper, and nickel-cobalt alloy), accomplished by a facile low-temperature ammonium carbonate treatment, for significantly improved hydrogen generation from neutral water. Various physicochemical characterization techniques including synchrotron X-ray absorption spectroscopy (XAS) and theory modeling demonstrate that the surface nitrogen modification does not change the chemical composition of the underlying transition metals. Notably, the resulting nitrogen-modified nickel framework (N-Ni) exhibits an extremely low overpotential of 64 mV at 10 mA cm, which is, to our knowledge, the best among those nonprecious electrocatalysts reported for hydrogen evolution at pH 7. Our combined experimental results and density functional theory (DFT) calculations reveal that the surface electron-rich nitrogen simultaneously facilitates the initial adsorption of water via the electron-deficient H atom and the subsequent dissociation of the electron-rich HO-H bond via H transfer to N on the nickel surface, beneficial to the overall hydrogen evolution process.
开发模仿自然光合作用的低成本混合水分解-生物合成系统，以实现太阳能到化学能的转化，对于未来的能源需求具有巨大的前景，但往往受到中性介质中非贵金属过渡金属催化剂表面动力学缓慢的析氢反应（HER）的限制。因此，合理地调整反应界面以提高中性 HER 催化动力学是非常可取的。在此，我们报告了一种通用的表面氮修饰多种过渡金属（例如铁、钴、镍、铜和镍钴合金）的方法，通过简便的低温碳酸铵处理来实现，从而显著提高了从中性水中的氢气生成效率。各种物理化学表征技术，包括同步辐射 X 射线吸收光谱（XAS）和理论建模，表明表面氮修饰不会改变底层过渡金属的化学成分。值得注意的是，所得的氮修饰镍骨架（N-Ni）在 10 mA cm 时表现出极低的过电位 64 mV，据我们所知，这是在 pH 7 下报道的用于析氢的非贵金属电催化剂中最好的。我们的综合实验结果和密度泛函理论（DFT）计算表明，表面富电子氮同时通过缺电子 H 原子促进水的初始吸附，以及通过 H 转移到镍表面上的 N 来促进富电子 HO-H 键的后续解离，有利于整体的析氢过程。
