He Yuan, Sun Chengwei, Alharbi Njud S, Yang Shubin, Chen Changlun
Key Laboratory of Photovoltaic and Energy Conservation Materials, Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Hefei 230031, PR China; University of Science and Technology of China, Hefei 230026, PR China.
Department of Biological Sciences, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia.
J Colloid Interface Sci. 2023 Nov 15;650(Pt A):151-160. doi: 10.1016/j.jcis.2023.06.102. Epub 2023 Jun 19.
Two-step water electrolysis has been proposed to tackle the ticklish H/O mixture problems in conventional alkaline water electrolysis recently. However, low buffering capacity of pure nickel hydroxide electrode as redox mediator limited practical application of two-step water electrolysis system. A high-capacity redox mediator (RM) is urgently needed to permit consecutive operation of two-step cycles and high-efficiency hydrogen evolution. Consequently, a high mass-loading cobalt-doped nickel hydroxide/active carbon cloth (NiCo-LDH/ACC) RM is synthesized via a facile electrochemical method. The proper Co doping can apparently enhance the conductivity and simultaneously remain the high-capacity of the electrode. Density functional theory results further confirms more negative values in redox potential of NiCo-LDH/ACC than Ni(OH)/ACC on account of the charge redistribution induced by Co doping, which can prevent the parasitic O evolution on RM electrode during decoupled H evolution step. As a result, the NiCo-LDH/ACC combined the superiorities of high-capacity Ni(OH)/ACC and high-conductivity Co(OH)/ACC, and the NiCo-LDH/ACC with 4:1 ratio of Ni to Co presented a large specific capacitance of 33.52F/cm for reversible charge-discharge and high buffering capacity with two-step H/O evolution duration of 1740 s at 10 mA/cm. The necessary input voltage (2.00 V) of the whole water electrolysis was broken into two smaller ones, 1.41 and 0.38 V, for H and O production, respectively. NiCo-LDH/ACC provided a favorable electrode material for the practical application of two-step water electrolysis system.
最近有人提出采用两步水电解来解决传统碱性水电解中棘手的氢氧混合问题。然而，纯氢氧化镍电极作为氧化还原介质的缓冲能力较低，限制了两步水电解系统的实际应用。迫切需要一种高容量的氧化还原介质（RM）来实现两步循环的连续运行和高效析氢。因此，通过一种简便的电化学方法合成了一种高质量负载的钴掺杂氢氧化镍/活性炭布（NiCo-LDH/ACC）RM。适当的钴掺杂可以显著提高导电性，同时保持电极的高容量。密度泛函理论结果进一步证实，由于钴掺杂引起的电荷重新分布，NiCo-LDH/ACC的氧化还原电位比Ni(OH)/ACC更负，这可以防止在解耦析氢步骤中RM电极上发生寄生析氧。结果，NiCo-LDH/ACC结合了高容量Ni(OH)/ACC和高导电性Co(OH)/ACC的优势，Ni与Co比例为4:1的NiCo-LDH/ACC在可逆充放电时表现出33.52F/cm的大比电容，在10mA/cm下具有1740s的两步氢氧析出持续时间的高缓冲容量。整个水电解所需的输入电压（2.00V）分别分解为用于产氢和产氧的两个较小电压，即1.41V和0.38V。NiCo-LDH/ACC为两步水电解系统的实际应用提供了一种良好的电极材料。
