Earth-Abundant Transition Metal Catalysts for HX Splitting

描述（由申请人提供）：确定和实施清洁，可持续和负担得起的能源对未来的环境和人类健康问题至关重要。可持续的以氢为基础的经济需要从质子介质（如H2O或矿物酸（HX））中生产氢，并与太阳能相结合。将质子介质转化为太阳能到氢的封闭催化循环必须满足两个技术障碍：1)质子还原生成二氢，2)阴离子氧化。HX生成H2的封闭循环既需要质子还原生成H2，又需要卤化物氧化生成X2。​利用化学陷阱促进X2形成的概念验证系统已经开发出来，然而，这些系统不适合用于能量存储。本提案旨在开发基于地球上丰富的第一排过渡金属的廉价催化剂，用于光化学HX分裂。如果成功，这项研究将构成一个封闭的太阳能-氢转换方案，其中矿物酸（HX）利用太阳能转化为H2和X2。所产生的氢可以用作燃料，或者通过小分子底物（如CO2）的氢化作为液体燃料隔离，或者直接用于氢燃料电池。为了实现开发太阳能制氢方案的目标，首先将开发能够质子还原的低价过渡金属配合物。同时，对金属二卤化物配合物的研究将允许确定卤化物氧化的临界要求。为了实现具有挑战性但必要的X2光消除，将设计配体以提供高氧化激发态的通道。对HX分裂的每个基本步骤——质子还原和卤化物氧化——的研究将阐明每个组成半反应所需的基本参数。根据HX分裂的每个基本步骤所需的配体特征，过渡金属催化剂将被设计为能够实现真正的HX分裂

DESCRIPTION (provided by applicant): Identification and implementation of clean, sustainable, and affordable energy sources is of paramount importance for both environmental and human health concerns in the future. Sustainable hydrogen-based economies require that hydrogen production from protic media, such as H2O or mineral acids (HX), be coupled to solar power. Closed catalytic cycles for solar-to-hydrogen energy conversion from protic media must meet two technological hurdles: 1) proton reduction to generate dihydrogen, and 2) anion oxidation. A closed cycle for generating H2 from HX requires both proton reduction to form H2 as well as halide oxidation to generate X2. Thus far, molecular catalysts for authentic HX splitting have not been developed. Proof-of-concept systems, which employ chemical traps to promote X2 formation have been developed, however, these systems are not amenable to use in energy storage. This proposal aims to develop inexpensive catalysts based on earth- abundant, first-row transition metals for photochemical HX splitting. If successful, the proposed research would constitute a closed solar-to-hydrogen conversion scheme, in which mineral acids (HX) are converted to H2 and X2 using solar power. The resultant hydrogen could be used as fuel, either by sequestration as a liquid fuel by hydrogenation of small molecule substrates such as CO2 or by being used directly in hydrogen fuel cells. To accomplish the goal of developing a solar-to-hydrogen scheme, low-valent transition metal complexes, capable of proton reduction will first be developed. Simultaneously, investigations of metal dihalide complexes will allow critical requirements for halide oxidation to be defined. To enable the challenging, but necessary, X2 photoelimination, ligands wil be designed to provide access to highly oxidizing excited states. Studies of each of the fundamental steps of HX splitting - proton reduction and halide oxidation - will elucidate fundamental parameters required for each of the constituent half reactions. Informed by the requisite ligand features for each of the fundamental steps of HX splitting, transition metal catalysts will be designed to enable authentic HX splitting photocatalysis to be achieved. PUBLIC HEALTH RELEVANCE: Identification and implementation of clean, sustainable, and affordable energy sources is of paramount importance for both environmental and human health concerns in the future. In 2005 it was estimated that particulate air pollution, whose major source in urban environments is automobile exhaust, is to blame for 500,000 deaths each year. Herein, I propose the development of novel transition metal catalysts for HX splitting, which would enable use of non-polluting hydrogen-based fuels and sever the connection between energy and petroleum-based fuels.