Sustainable Hydrogen Production from Seawater Electrolysis

电化学能够实现电能和化学能之间的高效直接转换，是实现净零能耗的关键。氢-氧（H2-O2）燃料电池是一项令人兴奋的电化学技术，它只需要清洁的水作为副产品就能高效地发电。支持该技术的绿色和可持续的氢气生产途径是使用可再生能源或多余的电力进行水电解；然而，这是一个能量上坡的过程，涉及阴极的析氢反应（HER）和阳极的析氧反应（OER）。虽然2电子HER相对容易，但4电子OER特别缓慢，并且在酸性条件下需要贵金属（Ir, Ru）作为催化剂。然而，最近取得了重大进展（包括申请人及其合作者的一些冒险工作），在碱性条件下更有效的OER，其中非贵金属催化剂如过渡金属（Ni, Fe）层状双氢氧化物（LDHs）被有效地使用。值得注意的是，水电解用于储存（作为H2）世界能源的很大一部分，水的分配问题将会出现，因为将需要大量的纯净水。另一方面，海水是地球上最丰富的水电解质原料，但其在水分解过程中的实施面临许多挑战，特别是阳极反应。海水电解中最严重的挑战是氯阴离子（按重量计海水中约3% NaCl）。在酸性条件下，OER反应的平衡电位（1.23 V）仅略低于ClER反应的平衡电位（1.36 V）；OER作为一个4电子反应需要高过电位，而ClER是一个容易的2电子反应，具有动力学优势，因此CIER可以与OER竞争。然而，在碱性条件下，OER的平衡电位明显降低，例如，pH=14时，OER的平衡电位为0.40 V；ClER的平衡电位变化不大（1.36 V），但现在必须考虑氯化物氧化反应（ClOR）生成的次氯酸盐（ClO-），因为后者在pH=14时的平衡电位相对较低，为0.88 V；现在很明显，在ClOR发生之前，OER工作的电位域有480 mV的显著差异。在上述背景下，这个令人兴奋的项目旨在将用于OER阳极和HER阴极的新催化剂（包括表面结构和层），阴离子交换膜，膜电极组装和反应器系统开发的新兴工作结合起来。为了确定制定低成本和高性能（活性和耐用）电极和膜电极组件（MEAs）的可行性，用于具有成本效益和可扩展的海水电解槽，以实现可持续的氢气生产，最大限度地提高资源和能源效率。这项工作雄心勃勃，风险也很高，因为海水电解非常有吸引力，但也极具挑战性，从竞争性氯化物氧化到腐蚀性环境，这需要高度选择性的电催化剂，在材料水平上具有良好的稳定性，以及精心设计的电极和界面，以促进质量传递（气泡去除），从而在反应器水平上维持高电流密度。然而，如果这项可行性研究取得成功，它将带来极大的回报，因为它为低成本、大规模、真正可持续的绿色制氢开辟了一个新的范例，为英国及其他地区提供可持续的净零排放。

Electrochemistry enables direct conversion between electrical and chemical energy with high efficiency, and is a key to achieving net zero. An exciting electrochemical technology is the hydrogen-oxygen (H2-O2) fuel cell that produces electricity at high efficiency with only clean water as the byproduct. A green and sustainable route for H2 production to support this technology is water electrolysis using renewable or excess electricity; however, it is an energetically uphill process involving the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. Whilst the 2-electron HER is relatively facile, the 4-electron OER is particularly sluggish and requires noble metals (Ir, Ru) as catalysts under acidic conditions. Nevertheless, recently significant progress has been made (including some adventurous work by the applicant and their collaborators) towards more efficient OER under alkaline conditions, where non-noble metal catalysts such as transition metal (Ni, Fe) layered double hydroxides (LDHs) were effectively used. Notably, for water electrolysis to be used to store (as H2) a substantial portion of the world's energy, water distribution issues will arise as vast amounts of purified water will be needed. On the other hand, seawater is the most abundant aqueous electrolyte feedstock on Earth, but its implementation in the water-splitting process presents many challenges, especially for the anodic reaction. The most serious challenges in seawater electrolysis are posed by the chloride anions (around 3% NaCl in seawater by weight). Under acidic conditions, the OER equilibrium potential (1.23 V) is only slightly (130 mV) lower than that (1.36 V) of the chlorine evolution reaction (ClER); and OER as a 4-electron reaction requires a high overpotential while ClER is a facile 2-electron reaction with a kinetic advantage, thus CIER can compete with OER. However, in alkaline conditions, the equilibrium potential of OER is significantly shifted lower, e.g., 0.40 V at pH=14; while that of ClER does not change so much (1.36 V) but now the hypochlorite (ClO-) formation from chloride oxidation reaction (ClOR) must be considered as the latter has a relatively lower equilibrium potential of 0.88 V at pH=14; clearly now there is a significant difference of 480 mV in potential domain for OER to work before ClOR occurs.Within the above context, this exciting project aims to draw together the nascent work on new catalysts (including surface structures and layers) for the OER anode and HER cathode, the anion exchange membrane, membrane-electrode-assembly and reactor system development, in order to determine the feasibility of formulating low-cost and high performance (active and durable) electrodes and membrane-electrode-assemblies (MEAs) for a cost-effective and scalable seawater electrolyser for sustainable hydrogen production with the maximum resource and energy efficiencies. The proposed work is highly ambitious and high risk, as seawater electrolysis is very attractive but extremely challenging, ranging from competitive chloride oxidation to corrosive environments, which require highly selective electrocatalysts together with good stability at material level, and well-engineered electrodes and interfaces to facilitate mass transport (gas bubble removal) to enable high current density to be sustained at reactor level. However, if this feasibility research is successful, it will be extremely rewarding as it opens a new paradigm for low cost, large scale, and truly sustainable green hydrogen production for delivering sustainable net zero for the UK and beyond.