氨水制氢液流电解池的构建及其提高能效与反应速度的机理研究

Ammonia (NH3) is increasingly viewed as a great hydrogen carrier, accordingly efficient and fast extraction of hydrogen from it becomes attractive. Theoretically electrolysis of aqueous ammonia only consumes 7.5% of the electricity generated from hydrogen fuel cell, and the only side product is nitrogen. However, up to date the energy efficiency, hydrogen generation rate and purity are not satisfactory. The major bottleneck is the difficulty of their simultaneous approaching satisfactions. The slow mass transfer and reaction rate of the anode side slows down the hydrogen production rate of cathode side due to the share of common electrolytes by both cells. A solution to this problem in past investigations was applying overpotential, but it may lead to low energy efficiency. Another option was using novel electrodes or catalysts, but they are often of high cost or lack of stable performance. This project proposes using flow electrolytic cells to overcome the bottleneck. Anode and cathode cells are separately operated wherein the concentration and flow rate are separately designed. This may strengthen convection and molecular diffusion and hence increase the overall reaction rate and energy efficiency. This project plans to build such cells and study energy efficiency and reaction kinetics and then perform modelling, which may promote hydrogen production either from on-board aqueous ammonia or waste water involving ammonia.

氨（NH3）被日益视作一种优良的氢能载体，故从氨中高效快速提取氢（H2）的技术也日显重要。氨水电解制氢在理论上只需氢燃料电池发电量的7.8%，只副产氮气(N2)，故近年来日渐引起重视，但至今为止其能效、制氢速度和纯度不够理想，主要瓶颈是能效与反应速度难以同步提高，阴阳两极共享电解质使得阳极端的低传质反应速度拉低了阴极端的氢气生成速度。以往主要解决方案之一是采用较高的超电势，但这会降低能效或有氧气(O2)产生；另一方案是开发新型电极或催化剂，但通常较昂贵或不够稳定。本项目提出采用液流电解池克服上述瓶颈，即阴阳两极不共享电解质，避免交叉干扰，各自独立控制浓度流速等参数强化分子扩散、对流传质与离子迁移，从而可同时各自降低电解质的导电和传质阻力，同步提高总括反应速度、能效和氢气纯度。为此将构建一个氨水液流电解池，对其能效和反应动力学机理进行研究，为车载氢源或利用含氨废水发电提供理论模型和设计依据。

氨（NH3）被日益视作一种优良的氢能载体，故从氨中高效快速提取氢（H2）的技术也日显重要。氨水电解制氢在理论上只需氢燃料电池发电量的7.8%，只副产氮气(N2)，故近年来日渐引起重视，但至今为止其能效、制氢速度和纯度不够理想，主要瓶颈是能效与反应速度难以同步提高，阴阳两极共享电解质使得阳极端的低传质反应速度拉低了阴极端的氢气生成速度。以往主要解决方案之一是采用较高的超电势，但这会降低能效或有氧气(O2)产生；另一方案是开发新型电极或催化剂，但通常较昂贵或不够稳定。.本项目创造性的采用了液流电解池克服上述瓶颈，即阴阳两极不共享电解质，避免交叉干扰，各自独立控制浓度流速等参数强化分子扩散、对流传质与离子迁移，从而同时各自降低了电解质的导电和传质阻力，同步提高了总括反应速度、能效和氢气纯度。.本项目还采用了铂-铱双金属构建创新型的催化电极，大幅度提高了催化效率，降低了催化电极中毒的几率，增加了电极使用的循环次数和寿命。基于双金属催化剂电极，本项目定量表征了电极的微观结构尺寸，研究了电极在实验和实用电流密度（1-100mA/cm2）操作条件下的能效和稳定性，并构建了氨水裂解制氢的电化学反应动力学模型，用来预测和指导氨水电解制氢的速率以及温度和流速对速率的影响。此外，还构建了氨水电解池的电能模型，用来指导和确定电解池双金属电极的电压、电流和电能质量的优化操作条件。.本项目成功构建了氨水液流电解池，制作了小微型原型机，并和下游氢气使用端的燃料电池以及上游的氨水供应罐等设备集成起来，运行良好，针对集成系统的能效进行了建模，热力学效率在75%以上，电耗少于燃料电池理论发电量的25%，未来可为车载氢源或利用含氨废水发电提供放大运行参考和放大计依据。