Catalase HPII of Escherichia coli is similar in sequence and structure to other catalases including the conservation of several residues on both the distal and proximal sides of the active center heme. The roles of many residues on the distal side of the heme have been well characterized. By contrast, very few residues on the proximal side of the heme or in the plane of the heme have been investigated. The primary goal of this thesis is to develop a better understanding of the role of the residues and structural features at the core of catalases and in the lateral access channel. The results demonstrate that a break in molecular symmetry does not have any functional significance. Replacing Ile274 with a Cys resulted in the heme being covalently linked to the protein through a Cys-vinyl bond which is hypersensitive to X-ray irradiation being largely degraded within seconds of exposure to the X-ray beam.

Catalase HPII of Escherichia coli is similar in sequence and structure to other catalases including the conservation of several residues on both the distal and proximal sides of the active center heme. The roles of many residues on the distal side of the heme have been well characterized. By contrast, very few residues on the proximal side of the heme or in the plane of the heme have been investigated. The primary goal of this thesis is to develop a better understanding of the role of the residues and structural features at the core of catalases and in the lateral access channel. The results demonstrate that a break in molecular symmetry does not have any functional significance. Replacing Ile274 with a Cys resulted in the heme being covalently linked to the protein through a Cys-vinyl bond which is hypersensitive to X-ray irradiation being largely degraded within seconds of exposure to the X-ray beam.

Li-O2 batteries have been attracting increasing attention and R&D efforts as promising power sources for electric vehicles (EVs) due to their significantly higher theoretical energy densities compared to conventional Li-ion batteries. The research presented in this thesis covers the investigation of factors influencing the decomposition of Li2O2, the development of highly active electrocatalysts, and the design of low-cost and easy-operation binder-free O2 electrodes for Li-O2 batteries. Being the main technique, SR-PXD was used both as a continuous light source to advance the electrochemical decomposition of Li2O2 under the X-ray illumination and an operando tool that allowed us to probe the degradation of Li2O2. Since XRD was intensively used in my thesis work, the effect of X-ray irradiation on the stability of Li2O2 was studied. The accelerating effect of X-rays on the electrochemical decomposition of Li2O2 was, for the first time, explored. The electrochemical decomposition rate of Li2O2 was proportional to the X-ray intensity used. It is proposed that the decomposition might involve a three-step reaction with [Li2O2]x+ and Li2-xO2* as intermediates, which followed pseudo-zero-order kinetics. Then, three electrocatalysts (Pt/MNT, Ru/MNT and Li2C8H2O6) were developed, which exhibited good electrocatalytic performances during the OER. Their activities were evaluated by following the Li2O2 decomposition in electrodes during the charging processes. In addition, the time-resolved OER kinetics for the electrocatalyst-containing Li-O2 cells charged galvanostatically and potentiostatically was systematically investigated using operando SR-PXD. It was found that a small amount of Pt or Ru decoration on the MNTs enhanced the OER efficiency in a Li-O2 cell. The Li2O2 decomposition of an electrode with 5 wt% Pt/MNT, 2 wt% Ru/MNT or Li2C8H2O6 in a Li-O2 cell followed pseudo-zero-order kinetics. Finally, a novel binder-free NCPE for Li-O2 batteries was presented. It displayed a bird’s nest microstructure, which could provide the self-standing electrode with considerable mechanic durability, fast O2 diffusion and enough space for the discharge product deposition. The NCPE contained N-containing functional groups, which may promote the electrochemical reactions.