• Energy Research

Nitrogen-doped graphene as a metal-free catalyst for oxygen reduction was synthesized by heat-treatment of graphene using ammonia. It was found that the optimum temperature was 900 °C. The resulting catalyst had a very high oxygen reduction reaction (ORR) activity through a four-electron transfer process in oxygen-saturated 0.1 M KOH. Most importantly, the electrocatalytic activity and durability of this material are comparable or better than the commercial Pt/C (loading: 4.85 µgPt cm−2). XPS characterization of these catalysts was tested to identify the active N species for ORR.

LiFePO4 has been a promising cathode material for rechargeable lithium ion batteries. Different secondary or impurity phases, forming during either synthesis or subsequent redox process under normal operating conditions, can have a significant impact on the performance of the electrode. The exploration of the electronic and chemical structures of impurity phases is crucial to understand such influence. We have embarked on a series of synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy studies for the element speciation in various impurity phase materials relevant to LiFePO4 for Li ion batteries. In the present report, soft-X-ray XANES spectra of Li K-edge, P L2,3-edge, O K-edge and Fe L2,3-edge have been obtained for LiFePO4 in crystalline, disordered and amorphous forms and some possible “impurities”, including LiPO3, Li4P2O7, Li3PO4, Fe3(PO4)2, FePO4, and Fe2O3. The results indicate that each element from different pure reference compounds exhibits unique spectral features in terms of energy position, shape and intensity of the resonances in its XANES. In addition, inverse partial fluorescence yield (IPFY) reveals the surface vs. bulk property of the specimens. Therefore, the spectral data provided here can be used as standards in the future for phase composition analysis.

A mixed conductive garnet/Li interface consisting of electronic conductive nanoparticles embedded in an ionic conductive network is constructed for dendrite-free solid garnet batteries.

A critical challenge for the commercialization of layer-structured nickel-rich lithium transition metal oxide cathodes for battery applications is their capacity and voltage fading, which originate from the disintegration and lattice phase transition of the cathode particles. The general approach of cathode particle surface modification could partially alleviate the degradation associated with surface processes, but it still fails to resolve this critical barrier. Here, we report that infusing the grain boundaries of cathode secondary particles with a solid electrolyte dramatically enhances the capacity retention and voltage stability of the cathode. We find that the solid electrolyte infused in the boundaries not only acts as a fast channel for lithium-ion transport, it also, more importantly, prevents penetration of the liquid electrolyte into the boundaries, and consequently eliminates the detrimental factors, which include cathode–liquid electrolyte interfacial reactions, intergranular cracking and layered-to-spinel phase transformation. This grain-boundary engineering approach provides design ideas for advanced cathodes for batteries. The development of Ni-rich layered lithium transition metal oxides is plagued by their voltage and capacity fading on battery cycling. Here, the authors demonstrate an effective approach to treat these problems by infusing a solid electrolyte into the grain boundaries of the secondary particles of these layered materials.

This review highlights the remaining challenges for LiFePO4in lithium-ion batteries and future olivine cathodes in Na-ion batteries.

AbstractOwing to the rapidly increasing consumption of fossil fuels, finding clean and reliable new energy sources is of the utmost importance. Thus, developing highly efficient and low‐cost catalysts for electrochemical reactions in energy conversion devices is crucial. Single‐atom catalysts (SACs) with maximum metal atom utilization efficiency and superior catalytic performance have attracted significant attention, especially for electrochemical reactions. However, because of the highly unsaturated coordination environment, the stability of SACs can be a challenge for practical applications. In this review, we will summarize the strategies to increase the stability of SACs and synthesizing stable SACs, as well as the application of SACs in electrochemical reactions. Finally, we offer a perspective on the development of advanced SACs through rational design and a deeper understanding of SACs with the help of in situ or operando techniques in electrochemical reactions.

Achieving a balance between lithium ion and vacant site contents plays a crucial role in obtaining optimal ionic conductivity in halide electrolytes, especially with a hexagonal close packing (hcp) anion framework.

AbstractA fuel cell is an energy conversion device that can continuously input fuel and oxidant into the device through an electrochemical reaction to release electrical energy. Although noble metals show good activity in fuel cell‐related electrochemical reactions, their ever‐increasing price considerably hinders their industrial application. Improvement of atom utilization efficiency is considered one of the most effective strategies to improve the mass activity of catalysts, and this allows for the use of fewer catalysts, saving greatly on the cost. Thus, single‐atom catalysts (SACs) with an atom utilization efficiency of 100% have been widely developed, which show remarkable performance in fuel cells. In this review, we will describe recent progress on the development of SACs for membrane electrode assembly of fuel cell applications. First, we will introduce several effective routes for the synthesis of SACs. The reaction mechanism of the involved reactions will also be introduced as it is highly determinant of the final activity. Then, we will systematically summarize the application of Pt group metal (PGM) and nonprecious group metal (non‐PGM) catalysts in membrane electrode assembly of fuel cells. This review will offer numerous experiences for developing potential industrialized fuel cell catalysts in the future.

Li-S batteries have been considered as next generation Li batteries due to their high theoretical energy density. Over the past few years, researchers have made significant efforts in breaking through critical bottlenecks which impede the commercialization of Li-S batteries. Beginning with a basic introduction to Li-S systems and their associated mechanism, this review will highlight the application of one specific carbon family, nitrogen-doped carbon materials in sulfur based cathodes. These materials will include nitrogen doped porous carbon, carbon nanotubes, nanofibers and graphene. The article will conclude with a summary of recent research efforts in this field as well as the future prospects for the use of nitrogen-doped carbon materials in Li-S batteries.