Nitrate enrichment, which is mainly caused by the over-utilization of fertilisers and industrial sewage discharge, is a major global engineering challenge because of its negative influence on the environment and human health. To solve this serious problem, many technologies, such as the activated sludge method, reverse osmosis, ion exchange, adsorption, and electrodialysis, have been developed to reduce the nitrate levels in water bodies. However, the applications of these traditional techniques are limited by several drawbacks, such as a long sludge retention time, slow kinetics, and undesirable by-products. From an environmental perspective, the most promising nitrate reduction technology is enabled to convert nitrate into benign N₂, and features low cost, high efficiency, and environmental friendliness. Recently, electrocatalytic nitrate reduction has been proven by satisfactory research achievements to be one of the most promising methods among these technologies. This review provides a comprehensive account of nitrate reduction using electrocatalysis methods. The fundamentals of electrocatalytic nitrate reduction, including the reaction mechanisms, reactor design principles, product detection methods, and performance evaluation methods, have been systematically summarised. A detailed introduction to electrocatalytic nitrate reduction on transition metals, especially noble metals and alloys, Cu-based electrocatalysts, and Fe-based electrocatalysts is provided, as they are essential for the accurate reporting of experimental results. The current challenges and potential opportunities in this field, including the innovation of material design systems, value-added product yields, and challenges for products beyond N₂ and large-scale sewage treatment, are highlighted.

Due to massively growing demand arising from energy storage systems, sodium ion batteries (SIBs) have been recognized as the most attractive alternative to the current commercialized lithium ion batteries (LIBs) owing to the wide availability and accessibility of sodium. Unfortunately, the low energy density, inferior power density and poor cycle life are still the main issues for SIBs in the current drive to push the entire technology forward to meet the benchmark requirements for commercialization. Over the past few years, tremendous efforts have been devoted to improving the performance of SIBs, in terms of higher energy density and longer cycling lifespans, by optimizing the electrode structure or the electrolyte composition. In particular, among the established anode systems, those materials, such as metals/alloys, phosphorus/phosphides, and metal oxides/sulfides/selenides, that typically deliver high theoretical sodium-storage capacities have received growing interest and achieved significant progress. Although some review articles on electrodes for SIBs have been published already, many new reports on these anode materials are constantly emerging, with more promising electrochemical performance achieved via novel structural design, surface modification, electrochemical performance testing techniques, etc. So, we herein summarize the most recent developments on these high-performance anode materials for SIBs in this review. Furthermore, the different reaction mechanisms, the challenges associated with these materials, and effective approaches to enhance performance are discussed. The prospects for future high-energy anodes in SIBs are also discussed.