In-situ studies of biomolecular assisted Li-air batteries and studies of biobased redox mediators and ORR catalysts

博士项目战略主题：可再生资源和清洁增长的生物科学锂空气电池（实验室）最近受到了极大的关注，因为它们的能量密度与化石燃料相当，而且比锂离子电池更环保，因为它们不含过渡金属。典型的非水实验室依靠氧还原反应（ORR）来放电。氧化还原介质（RMs）通常用于协助阴极表面和O2之间的电子转移，降低电池过电位并控制放电产物的形成速率。氧化还原活性生物分子在自然界的能量吸收过程中起着至关重要的作用，通常作为辅因子与酶结合，在实验室中经常被用作RM。例如，醌类，如DBBQ、维生素K2或酶Q10，已被测试为RMs，取得了不同程度的成功。ORR生物催化剂，如血红素（血红蛋白的辅助因子）和酶，如来自Tramtes versicolor （LacTv）的漆酶，可以通过为排放产物的形成/分解提供稳定的中间体，进一步提高实验室的能源效率。生物ORR催化剂的活性取决于反应发生的介质，这影响了它们溶剂化氧和结合能的能力。这一点尤其重要，因为实验室是在有机电解质中工作的，而不是在生物系统的水溶液中。放电产物的速率和性质将受到电池内pH值和电子传递速率的影响，而电子传递速率又取决于所使用的电解质、速率和催化剂/RM的类型。目前，生物基RM/ORR催化剂在电池装置中的活性机理研究非常有限。为了建立有助于生物分子辅助实验室发展的结构-功能关系，需要新的原位表征技术。该项目的目的是发展原位x射线衍射和核磁共振波谱技术，以研究生物分子ORR催化剂的综合目录。有了这些新工具，我们的目标是通过筛选潜在的ORR催化剂和RMs库，如卟啉、黄素、吩那嗪、酞菁素和与这些辅助因子结合的酶，如细胞色素c氧化酶（CcO）、单脱氢抗坏血酸还原酶（MDAR）或NADH氧化酶，开发基于可持续来源的生物分子的优化实验室。在电池设置中，可溶辅助因子和接枝到电极上的酶之间的氧结合特性的差异以及对整体性能的影响也将被研究。这将使我们能够研究调节氧化还原介质活性的重要特性，如扩散率、平衡氧化还原电位、充电状态和电池运行过程中的降解途径。研究具有催化功能的氧化还原活性生物分子开辟了一条新的途径，高性能的RMs和ORR催化剂由可持续的、具有成本效益的材料制成，如可回收的生物废物（如血液废物或天然酶）。这两个方面都与BBSRC的战略主题生物科学促进可再生资源和清洁增长密切相关，该主题旨在通过减少对化石燃料的依赖来改变一系列行业，从而帮助实现国际气候变化目标。

PhD project strategic theme: Bioscience for renewable resources and clean growthLi-air batteries (LABs) have gained significant attention lately due to their comparable energy densities to fossil fuels, with the added advantage of being greener than Lithium-ion batteries, as they contain no transition metals. Typical non-aqueous LABs rely on an oxygen reduction reaction (ORR) to discharge. Redox mediators (RMs) are often used to assist in the electron transfer between the cathode surface and O2, lowering the battery overpotential and controlling the rate of formation of the discharge products. Redox-active biomolecules, which play vital roles in energy assimilating processes in nature and often bind to enzymes as cofactors, are often used as RM in LABs. For instance, Quinones, such as DBBQ, Vitamin K2 or Enzyme Q10 have been tested as RMs with varying success. ORR biocatalysts, such as heme (haemoglobin's co-factor), and enzymes, such as laccase from Tramtes versicolor (LacTv), can be used to further increase the energy efficiency in LABs by providing stable intermediates to the formation/decomposition of the discharge product. The activity of biological ORR catalysts depends on the media where the reaction takes place, which affects their ability to solvate oxygen and binding energetics. This is particularly important since LABS operate in organic-based electrolytes, in contrast to the aqueous solutions of biological systems. The rate and properties of discharge product will be influenced by the pH and electron transfer rate in the cell, which in turn depends on the electrolyte, rate and type of catalyst/RM used.Currently, mechanistic studies of the activity of bio-based RM/ORR catalysts in battery set-ups is very limited. In order to establish a structure-function relationship that would help the development of biomolecular-assisted LABs, novel in-situ characterization techniques are required. The aim of this project is to develop in-situ X-ray Diffraction and Nuclear Magnetic Resonance Spectroscopies with which a comprehensive catalogue of biomolecular ORR catalysts can be studied. With these novel tools, we aim to develop optimized LABs based on sustainably sourced biomolecules by screening a library of potential ORR catalysts and RMs such as porphyrins, flavins, phenazines, phthalocyanins and enzymes to which these co-factors are bonded such as cytochrome c oxidase (CcO), monodehydroascorbate reductase (MDAR) or NADH oxidase. The differences of oxygen binding characteristics between soluble co-factors and enzymes grafted onto the electrodes in the battery setup and the effect to the overall performance will also be studied. These will allow us to study important properties regulating the activity of redox mediators, such as diffusivity, equilibrium redox potential, state of charge, and degradation pathways during battery operation. Studying redox active biomolecules with catalytic functions opens up a new path high performance RMs and ORR catalysts made of sustainable, cost-effective materials such as recyclable bio-waste (e.g. blood waste or natural enzymes). Both of these aspects tie in well with the BBSRC strategic theme Bioscience for renewable resources and clean growth, which aims to transform a range of industries by reducing the reliance on fossil fuels and thereby help to meet international climate change targets.