储氢、供氢新概念-电解液氨制氢及其反应机理

Ammonia is regarded as a kind of hydrogen carrier with high hydrogen capacity.It exhibits desirable characteristics of facile storage, low price and along with non-greenhouse gas.But the high decomposition temperature limits its application as hydrogen storage material.The theoretical electrolysis voltage of liquid ammonia at 298 K is calculated by 0.077 V. The electrochemical technique is a promising method to realize the convenient and econimic decomposition of ammonia to hydrogen.In this project, a fundamental research will be performed on the electrolysis of liquid ammonia based on a new concept by using metal amide or ammonium salt as the supporting electrolyte for generation of hydrogen and nitrogen. The reasonable electrolysis experimental and analytical system will be built up on the basis of a three-electrodes electrolysis cell which could bear high pressure and low temperature,so as to investigate the hydrogen (or nitrogen) evolution reaction process on different metal electrodes in liquid ammonia. We intend to explore the rate-limited step as well as the kinetic reaction mechanism of hydrogen (or nitrogen) evolution reaction by acquiring the corresponding electrochemical and kinetic parameters.On the basis of the reaction mechanism, the desirable (noble) metal electrode materials with high catalytic activity and stability as well as low over-potential will be prepared by reasonable selection and design of the electrocatalyst system. Moreover, we will make a systematical research into the relationship among various factors, such as the substrate, the composition of electroplating solution, the loading amount and ratio of the (noble) metals, the surface area and morphology as well as the parameters of the electrodeposition process, with the hydrogen or nitrogen evolution reaction and the over-potential. Important influence factors on the electrolysis efficiency such as temperature, insulator material for the inner cell, electrolyte, electrocatalyst, and so on will be discussed in detail.The overpotential will be decreased so as to realize the high efficiency electrolysis of liquid ammonia. Conduction of this research will be helpful for the development of electrochemical decomposition of liquid ammonia to be a safe, efficient and economic hydrogen storage and supply technology.

氨是一种富氢载体,易于存储、价格低廉,且不会带来温室气体,但分解温度过高限制了其作为储氢材料的应用。298 K时液氨的理论分解电压为0.077 V,电化学方法有望实现便捷、经济的氨分解制氢。本项目拟建立耐压、耐低温三电极液氨电解池实验与分析体系,利用金属氨基化合物或铵盐作为支持电解质电解液氨制备氢气和氮气,研究各种金属电极材料在液氨中的析氢或析氮反应过程,获得各种电化学和动力学参数,探讨反应决速步骤并揭示可能的反应机理;结合反应机理合理选择并设计制备具有高催化活性和稳定性、低过电位的（贵）金属电极材料,建立基体材料、镀液组分、金属沉积量及比例、电极比表面积和表面形貌等参数与析氢或析氮性能以及过电位的关系;探讨温度、内衬材料、电解质以及电催化剂对电解效率的影响,降低欧姆损耗与反应过电位,优化电解池,实现液氨的高效电解。本研究将有助于电解液氨成为一种安全、高效、经济的储氢新技术。

成功地设计并建立起一套耐高压和低温三电极液氨电解池，搭建起适宜液氨传输的氨真空系统，结合电化学工作站、高精度压力传感器、气相色谱等表征手段，实现了科学、合理地电解液氨实验的定性、定量分析。.成功地合成了用于液氨电解的碱金属氨基化合物电解质单相（KNH2，KLi3(NH2)4等）。首次系统地调查了显碱性的碱金属氨基化合物及显酸性的铵盐（NH4I，NH4Br，NH4Cl，NH4NO3）以及显中性的钾盐（KPF6）对电解液氨体系电解效率、电流密度、体系内阻、析氢速率以及极化曲线等的影响。这一结果对发展电解液氨成为一种安全、高效、经济的储氢、供氢新技术具有重要推动力。.为了降低电极过电位，我们制备了单金属催化剂（Pt black、Rh）、双金属催化剂（RhPt）以及三金属催化剂（RhPtIr）作为电解液氨体系阳极催化剂，以NH4Cl做为支持电解质对催化剂性能进行了分析。探讨各类型催化剂对电解液氨体系电极活性和电化学稳定性能的影响。研究表明，三金属催化剂电极（RhPtIr）效果最为显著，表现出最低的液氨最小分解电势(0.47 V)以及最高的电流密度（46.9 mA/cm2，2.0 V）。探讨了以Cr-MIL-101金属有机骨架担载贵金属催化剂电催化氧化氨的应用前景。此外为了纯化氢气产物，优化了利用碱金属氢化物在温和条件下快速去除氨气的方法。