Platinum-based catalysts have been considered the most effective electrocatalysts for the hydrogen evolution reaction in water splitting. However, platinum utilization in these electrocatalysts is extremely low, as the active sites are only located on the surface of the catalyst particles. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their efficiency by utilizing nearly all platinum atoms. Here we report on a practical synthesis method to produce isolated single platinum atoms and clusters using the atomic layer deposition technique. The single platinum atom catalysts are investigated for the hydrogen evolution reaction, where they exhibit significantly enhanced catalytic activity (up to 37 times) and high stability in comparison with the state-of-the-art commercial platinum/carbon catalysts. The X-ray absorption fine structure and density functional theory analyses indicate that the partially unoccupied density of states of the platinum atoms’ 5d orbitals on the nitrogen-doped graphene are responsible for the excellent performance.

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 µg_Pt cm⁻²). XPS characterization of these catalysts was tested to identify the active N species for ORR.

Olivine-structured LiFePO₄ has been the focus of research in developing low cost, high performance cathode materials for lithium ion batteries. Various processes have been developed to synthesize LiFePO₄ or C/LiFePO₄ (carbon coating on LiFePO₄), and some of them are being used to mass produce C/LiFePO₄ at the commercial or pilot scale. Due to the low intrinsic electronic and ionic conductivities of LiFePO₄, the decrease of particle size and the nano-layer of carbon coating on LiFePO₄ particle surfaces are necessary to achieve a high electrochemical performance. Significant progress has been made in understanding and controlling phase purity, particle size and carbon coating of the C/LiFePO₄ composite material in the past. However, there are still many challenges in achieving a high quality product with high consistency. In this review, we summarize some of the recent progress and advances based on selected reports from peer-reviewed journal publications. Several typical synthesis methods and the effect of carbon coating quality on the properties of C/LiFePO₄ composite are reviewed. An insight into the future research and further development of C/LiFePO₄ composite is also discussed.

Platinum-nanoparticle-based catalysts are widely used in many important chemical processes and automobile industries. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their use efficiency, however, very challenging. Here we report a practical synthesis for isolated single Pt atoms anchored to graphene nanosheet using the atomic layer deposition (ALD) technique. ALD offers the capability of precise control of catalyst size span from single atom, subnanometer cluster to nanoparticle. The single-atom catalysts exhibit significantly improved catalytic activity (up to 10 times) over that of the state-of-the-art commercial Pt/C catalyst. X-ray absorption fine structure (XAFS) analyses reveal that the low-coordination and partially unoccupied densities of states of 5d orbital of Pt atoms are responsible for the excellent performance. This work is anticipated to form the basis for the exploration of a next generation of highly efficient single-atom catalysts for various applications.

Halide solid-state electrolytes (SSEs) with high room-temperature ionic conductivity (>10⁻³ S cm⁻¹), wide electrochemical windows, and good compatibility toward oxide cathode materials have achieved impressive progress and attracted significant attention for application in all-solid-state lithium batteries (ASSLBs). This review presents an overview of halide SSEs, including their development, structure, ionic conductivity, chemical stability, and current limitations. Firstly, we give a brief overview of the historical development of halide-based SSEs, followed by an introduction to the different types of halide SSEs. From a practical point of view, the synthesis methods, especially scalable liquid-phase synthesis, are intensively discussed. Then, the associated stability issues involving basic structure stability, air/humidity stability, and electrochemical stability (electrolyte/SSE interface and electrochemical stability window) are also discussed in detail. Comprehensive coverage and thorough understanding of the properties of halide SSEs are provided and it is expected to help guide the development of future SSEs towards ASSLBs for energy storage applications.