Natural solar cells and their geochemical implications

技术描述：光电化学过程在地球上的作用？美国的早期历史尚不清楚。许多常见的氧化物和硫化物矿物具有光活性，能够驱动自然光氧化还原过程。该提案讨论了地球历史上的几个重大事件，如带状铁形成和氧气的兴起，这些光化学活性矿物可能对这些事件有所贡献。该项目特别关注自然光电化学中的一个新概念：耦合矿物系统。在太阳能研究中，光化学水分解引起了人们极大的兴趣。利用阳光和水形成O2和H2。这样的过程通常效率很低，但是经过设计？串联细胞?其中已经构建了两个半导体，每个半导体吸收不同的光波长，大大提高了整个光催化过程的效率。我们在赤铁矿-黄铁矿串联电池的初始实验中测量的光化学电流密度（这可以预期在自然界中形成，作为早期黄铁矿氧化的简单结果）与带状铁地层中铁的沉积速率和火星随时间的水分流失率惊人地相似。因此，研究一些可能自然产生的矿物串联细胞系统的时机似乎已经成熟，以便量化基于矿物的光化学可能在多大程度上推动了重要的早期地球和行星过程。我们建议研究这种天然光电化学电池的行为和性质。我们打算了解水被氧化和氢气产生的速率，其他常见的水溶性溶质被氧化或还原的速率，这些过程所需的矿物性质，评估一小组在早期地球上可能很重要的矿物系统，并研究不同的pO2、光强、pH、温度以及水和固体成分对整个光电化学过程的影响。非技术解释：虽然半导体矿物在地球自然过程中的作用具有地质学意义，但矿物半导体作为光催化剂的基本特性可能对太阳能技术的发展具有最重要的意义。如果能开发出一种太阳能光催化系统，合理有效地生产燃料（化学储存的能量），这种技术？从长远来看，它是否真的会影响全球能源格局？一定是用地球上丰富的材料建造的。铁和锰的氧化物和硫化物是常见的，而地球上根本没有足够的铂来用作这种系统的电极/催化剂。从中长期能源安全（更不用说气候变化）的角度来看，本提案所描述的这种燃料发电技术需要更好地研究、改进和实施。PI在基础地球化学研究以及与从事太阳能研究的科学家一起工作方面都有经验，并且该提案中对串联电池矿物系统的改进理解同样适用于地球化学和太阳能技术。

Technical description:The role of photoelectrochemical processes in Earth?s early history is not well understood. Many common oxide and sulfide minerals are photoactive and capable of driving natural photoredox processes. The proposal discusses several major events in Earth history, such as banded iron formations and the rise of oxygen, to which such photochemically active minerals might have contributed. The project focuses in particular on a new concept in natural photoelectrochemistry: coupled-mineral systems.In solar energy research, there is a great deal of interest in photochemical water splitting ? the formation of O2 and H2 using sunlight and water. Such processes are usually quite inefficient, but engineered ?tandem cells? have been constructed in which two semiconductors, each absorbing a different light wavelength, greatly improve the efficiency of the overall photocatalytic process. The photochemical current densities that we measured in initial experiments with hematite-pyrite tandem cell (which can be expected to form in nature as the simple consequence of incipient pyrite oxidation) are surprisingly comparable to the deposition rates of iron in banded iron formations and the rate of water loss from Mars over time. The time seems ripe, therefore, to study a few likely naturally-occurring mineral tandem cell systems in order to quantify the extent to which mineral-based photochemistry might have driven important early-Earth and planetary processes.We propose to investigate the behavior and properties of such natural photo-electrochemical cells. We intend to understand the rates at which water can be oxidized and hydrogen produced, the rates at which other common aqueous solutes can be oxidized or reduced, the mineral properties needed for such processes, assess a small set of mineral systems that could have been important on early Earth, and investigate the effects of variable pO2, light intensity, pH, temperature, and both aqueous and solid compositions on the overall photoelectrochemical process. Non-technical explanation:While the role of semiconducting minerals in natural processes of the Earth is of geological interest, the fundamental properties of mineral semiconductors as photocatalysts are probably of greatest significance in the development of solar energy technology. If a solar photocatalytic system can be developed that produces fuels (chemically stored energy) reasonably efficiently, such technology ? if it is to truly impact the global energy picture in the long run ? must be constructed of Earth-abundant materials. Iron and manganese oxides and sulfides are common, whereas there is simply not enough platinum on Earth to be used as electrodes/catalyst for such systems. From the point of view of medium- to long-term energy security (not to mention climate change), such fuel-generating technologies as described in this proposal need to be better studied, improved, and implemented. The PI has experience both in fundamental geochemistry research as well as with scientists working on solar energy, and the improved understanding of the tandem-cell mineral systems in this proposal has applications equally in geochemistry and solar energy technology.