The use of conductive frameworks as the host scaffold to obtain nanostructured sulfur cathodes is an efficient way to increase the sulfur utilization for redox reaction in Li‐S batteries with large discharge capacity and high energy density. However, due to dynamical interfaces driven by phase evolution between the conductive hosts and S‐containing guests during cycling, the cathode still faces poor stability. Herein, the use of O‐/N‐containing nanocarbon as the conductive host sheds a light on the role of the dynamic interface between the carbon host and S‐containing guest for a stable Li‐S cell. The outstanding reversibility and stability of N‐doped C/S cathodes are attributed to the favorable guest‐host interaction at the electron‐modified interface, manifesting as (i) a chemical gradient to adsorb polar polysulfides and (ii) ameliorative deposition and recharging of Li2S on the region of electron‐rich pyridinic N and a graphene domain surrounding quaternary N. Highly reversible, efficient and stable Li storage properties such as mitigated polarization and charge barrier, high capacity of 1370 and 964 mAh g−1 at 0.1 and 1.0 C, respectively, and 70% of capacity retention after 200 cycles are achieved. Mechanistic insight into the capacity fading inspires the rational design on electrodes for high‐performance electrochemical systems.

We performed ab initio DFT+U calculations to explore the interaction between methane and iron oxide oxygen carriers for chemical looping reaction systems. The adsorption of CH4 and CHx (x = 0-3) radicals on α-Fe2O3(001), and the influence of oxygen vacancies at the top surface and on the subsurface on the adsorption properties of the radicals was investigated. The adsorption strength for CH4 and C radicals at the top of the α-Fe2O3(001) surface in the presence of oxygen vacancies is lower than that on the stoichiometric surface. However, for methyl (CH3), methylene (CH2) and methine (CH) radicals, it is correspondingly higher. In contrast, the oxygen vacancy formation on the subsurface not only increases the adsorption strength of CH3, CH2 and CH radicals, but also facilitates C radical adsorption. We found that oxygen vacancies significantly affect the adsorption configuration of CHx radicals, and determine the probability of finding an adsorbed species in the stoichiometric region and the defective region at the surface. With the obtained adsorption geometries and energetics of these species adsorbed on the surface, we extend the analysis to CH4 dissociation under chemical looping reforming conditions. The distribution of adsorbed CH4 and CHx (x = 0-3) radicals is calculated and analyzed which reveals the relationship between adsorbed CHx radical configuration and oxygen vacancies in iron oxide. Also, the oxygen vacancies can significantly facilitate CH4 activation by lowering the dissociation barriers of CH3, CH2 and CH radicals. However, when the oxygen vacancy concentration reaches 2.67%, increasing the oxygen vacancy concentration cannot continue to lower the CH dissociation barrier. The study provides fundamental insights into the mechanism of CH4 dissociation on iron based oxygen carriers and also provide guidance to design more efficient oxygen carriers.

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We perform ab initio DFT+U calculations and experimental studies of the partial oxidation of methane to syngas on iron oxide oxygen carriers to elucidate the role of oxygen vacancies in oxygen carrier reactivity. In particular, we explore the effect of oxygen vacancy concentration on sequential processes of methane dehydrogenation, and oxidation with lattice oxygen. We find that when CH adsorbs onto Fe atop sites without neighboring oxygen vacancies, it dehydrogenates with CH radicals remaining on the same site and evolves into COvia the complete oxidation pathway. In the presence of oxygen vacancies, on the other hand, the formed methyl (CH) prefers to migrate onto the vacancy site while the H from CH dehydrogenation remains on the original Fe atop site, and evolves into CO via the partial oxidation pathway. The oxygen vacancies created in the oxidation process can be healed by lattice oxygen diffusion from the subsurface to the surface vacancy sites, and it is found that the outward diffusion of lattice oxygen atoms is more favorable than the horizontal diffusion on the same layer. Based on the proposed mechanism and energy profile, we identify the rate-limiting steps of the partial oxidation and complete oxidation pathways. Also, we find that increasing the oxygen vacancy concentration not only lowers the barriers of CH dehydrogenation but also the cleavage energy of Fe-C bonds. However, the barrier of the rate-limiting step cannot further decrease when the oxygen vacancy concentration reaches 2.5%. The fundamental insight into the oxygen vacancy effect on CH oxidation with iron oxide oxygen carriers can help guide the design and development of more efficient oxygen carriers and CLPO processes.

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The cyclic redox reactivity of metal oxides plays an important role in many energy fields such as fuel cells, photocatalysis, and chemical looping. In chemical looping systems, oxygen carriers are required to have high reactivity, recyclability, and high oxygen carrying capacity. We utilize catalytic lanthanum dopants to dramatically change the reactivity with carbonaceous fuels while maintaining or even improving the recyclability of iron-based oxygen carriers. A low concentration of La dopant is applied to maintain the high oxygen carrying capacity. These results are substantiated by ab initio DFT+U and thermochemistry analysis and will have a significant impact on future chemical looping oxygen carrier design.

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