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Abstract: Layered manganese oxides adopting pre-accommodated cations have drawn tremendous interest for the application as cathodes in aqueous zinc-ion batteries (AZIBs) owing to their open 2D channels for fast ion-diffusion and mild phase transition upon topochemical (de)intercalation processes. However, it is inevitable to see these “pillar” cations leaching from the hosts owing to the loose interaction with negatively charged Helmholtz planes within the hosts and shearing/bulking effects in 2D structures upon guest species (de)intercalation, which implies a limited modulation to prevent them from rapid performance decay. Herein, a new class of layered manganese oxides, Mg0.9Mn3O7·2.7H2O, is proposed for the first time, aims to achieve a robust cathode for high-performance AZIBs. The cathode can deliver a high capacity of 312 mAh g−1 at 0.2 A g−1 and exceptional cycling stability with 92% capacity retention after 5 000 cycles at 5 A g−1. The comprehensive characterizations elucidate its peculiar motif of pined Mg-□Mn-Mg dumbbell configuration along with interstratified hydrogen bond responsible for less Mn migration/dissolution and quasi-zero-strain characters. The revealed new structure-function insights can open up an avenue toward the rational design of superstructural cathodes for reversible AZIBs.

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Abstract: Layered hydroxides have shown superior catalytic activity for the electrocatalytic organic compound oxidation reaction. However, metal leaching can lead to uncontrollable structural phase transformation. Here, we report a Cr-Ni(OH)2 electrocatalyst as a model of a pre-catalyst for the identification of the structure-performance relationship. The optimized electrocatalyst delivered superb performances, i.e., a low potential of 1.38 V (versus reversible hydrogen electrode [RHE]) to reach 100 mA cm−2 and stable activity over 200 h at 10 mA cm−2. In situ analyses and theoretical calculations demonstrate that well-tuned electronic structures and the superhydrophilic-superaerophobic surface can enable rapid urea oxidation reaction (UOR) kinetics, which reduces the specific adsorption OH− and significantly depresses Cr dopants leaching, and this helps to maintain high UOR performance. Furthermore, the crucial role of mass transfer improvement to alleviate the structural decay under high potentials is disclosed.

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Abstract: Despite progress of functionalized separator in preventing the shuttle effect and promoting the sulfur utilization, the precise and non-destructive investigation of structure-function-performance associativity remains limited so far in Li-S batteries. Here, we build consecutive multiscale analysis via combining X-ray absorption fine structure (XAFS) and X-ray computational tomography (CT) techniques to precisely visit the structure-function-performance relationship. XAFS measurement offers the atomic scale changes in the chemical structure and environment. Moreover, a non-destructive technique of X-ray CT proves the functionalized separator role for microscopic scale, which is powerful chaining to bridge the chemical structures of the materials with the overall performance modulation of cells. Benefiting from this consecutive multiscale analysis, we report that the uniform doping of Sr2+ into the perovskite LaMnO3-δ material changes the Mn oxidation states and conductivity (chemical structure), leading to effective lithium polysulfide trapping and accelerated sulfur redox (separator function), and resulting in outstanding cell performance.

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Abstract: The research for surface active sites with outstanding catalytic activity and selectivity is continuing apace. The rationally designed catalyst with optimised energy level and geometric configuration is key to achieving novel reaction pathways with superior performance. Compared to the conventional supported nanomaterials as catalysts, single atomic site catalysts (SASCs) not only inherit the excellent recyclability but are also featured with ultimate atom efficiency, high structural uniformity and tunable coordination environment. These great advantages of SASCs are due to their unique atomic dispersion nature that preserves features of both heterogeneous and homogeneous catalysts. Especially the homogeneity of SASC enables convincing identification and characterisation of real active sites, making it an ideal platform to establish the definitive structure-activity relationship and to validate reaction mechanisms. Therefore, rational designed SASC has become the most prominent material to fabricate desired active sites with outstanding catalytic activity and selectivity. In this thesis, chemical synthesis strategies and characterisation techniques for SASCs are carefully reviewed. The limitations and future perspectives from a subjective view of the current methodology are discussed in detail as well. As inspired by pioneers’ work, rational designed Ru and Cu SASCs are prepared to investigate their distinct relationships between catalyst structures and reaction behaviours during CO oxidation reaction. With the help of combined in situ characterisation techniques, the structural evolution of active sites for both Ru and Cu catalysts were carefully studied. In the first project, the ultimate rational design of Ru active centre is realised by building surface single-sites to mimic molecular Ru catalysts. Inspired by a homogeneous Ru(II) complex, an air-stable surface -[bipy-Ru(II)(CO)2Cl2] single-site is designed through precise engineering of geometric and electronic structures from -[bipy-Ru(III)Cl4]- site. Such Ru(II) single-site enable oxidation of CO while the Ru(III) site is completely inert, providing an excellent prototype of the synthetic strategy which is generally applicable to transition metals. The second project focuses on the electronic metal-support interactions (EMSI) which describe electron flow between metal sites and a metal oxide support. For CuO-CeO2 catalysts, the electron withdrawing effect on Cu species introduced by electrophilic Ce4+ is maximised for atomically dispersed Cu sites over CeO2 surface. Experiment evidence shows the energy levels of 3d orbitals of isolated Cu(I)/(II) sites are decreased by Ce4+ cations in the support framework. It is demonstrated by in situ study that a [Cu(I)O2]3- site on CeO2 could selectively adsorb molecular O2 and form a rarely reported electrophilic 2-O2 species, leading to ten times higher activity than CuO clusters in CO oxidation. The third project is derived from the previous study of CuO-CeO2 catalysts, in which an unbalanced electron transfer between Cu and Ce is observed for CuO clusters dominant samples. To explain the reaction pathway of CeO2 supported CuO clusters in CO oxidation, an electronic metal-support-carbon interaction (EMSCI) based on EMSI is proposed. In the CuO-CeO2 redox, an additional flow of electron from metallic Cu to surface carbon species is observed by combined in situ studies, providing a complete picture of the mass and electron flow in the catalytic redox cycles.

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Abstract: It remains a challenge to develop efficient electrocatalysts in neutral media for hydrogen evolution reaction (HER) due to the sluggish kinetics and switch of the rate determining step. Although metal phosphides are widely used HER catalysts, their structural stability is an issue due to oxidization, and the HER performance in neutral media requires improvement. Herein, a new material, i.e., grapevine‐shaped N‐doped iron phosphide on carbon nanotubes, as an efficient HER catalyst in neutral media is developed. The optimized catalyst shows an overpotential of 256 mV at a large current density of 65 mA cm−2, which is even 10 mV lower than that of the commercial 20% Pt/C catalyst. The excellent performance of the catalyst is further studied by combined computational and experimental techniques, which proves that the interaction between nitrogen and iron phosphides can provide more efficient active structures and stabilize the metal phosphide electrocatalysts for HER.