Selenium (Se), as an important quasi-metal element, has attracted much attention in the fields of thin-film solar cells, electrocatalysts and energy storage applications, due to its unique physical and chemical properties. However, the electrochemical behavior of Se in different systems from electrolytic cell to battery are complex and not fully understood. In this article, we focus on the electrochemical processes of Se in aqueous solutions, molten salts and ionic liquid electrolytes, as well as the application of Se-containing materials in energy storage. Initially, the electrochemical behaviors of Se-containing species in different systems are comprehensively summarized to understand the complexity of the kinetic processes and guide the Se electrodeposition. Then, the relationship between the deposition conditions and resulting structure and morphology of electrodeposited Se is discussed, so as to regulate the morphology and composition of the products. Finally, the advanced energy storage applications of Se in thin-film solar cells and secondary batteries are reviewed, and the electrochemical reaction processes of Se are systematically comprehended in monovalent and multivalent metal-ion batteries. Based on understanding the fundamental electrochemistry mechanism, the future development directions of Se-containing materials are considered in view of the in-depth review of reaction kinetics and energy storage applications.

Rechargeable Al-ion batteries (AIBs) are considered as one of the most fascinating energy storage systems due to abundant Al resource and low cost. However, the cycling stability is subjected to critical problems for using Al foil as negative electrode, including Al dendrites, corrosion and pulverization. For addressing these problems, here a lightweight self-supporting N-doped carbon rod array (NCRA) is demonstrated for a long-life negative electrode in AIBs. Experimental analysis and first-principle calculations reveal the storage mechanism involving the induced deposition of N-containing function groups to Al as well as the ideal skeleton of the NCRA matrix for Al plating/stripping, which is favorable for regulating Al nucleation and suppressing dendrites growth. Compared with the Al foil, the NCRA exhibits lower areal mass density (~ 72% of Al foil), smaller thickness (40% of Al foil), but much longer cycle life (> 4 times of Al foil). Benefiting from the remarkable stability of the array structure, symmetric cells show excellent cycling stability with small voltage hysteresis (~ 80 mV) and meanwhile there are no corrosion and pulverization problems even after cycled for 120 hours. Besides, full cells also manifest long lifespan (1,500 cycles) and increased Coulombic efficiency (100±1%).

To achieve stable positive electrode for promoting the overall electrochemical performance of Al batteries (ABs), here novel cobalt boride (CoB) nanoclusters are synthesized to construct composite electrodes with few-layer graphene (FLG). Due to the presence of amorphous channels in the employed CoB nanoclusters, the ABs with FLG/CoB composite positive electrodes exhibit high rate capability and both mechanical and electrochemical stability in the ABs. With assistance of in situ scanning electron microscopy (SEM), the observation results suggest that the positive electrode of CoB nanoclusters holds almost ignorable volume variation upon electrochemical processes, which substantially alleviates the massive electrode expansion induced by the anion intercalation in the composite positive electrode. Interestingly, the composite positive electrodes provide stable reversible energy storage capability within a broadened temperature range (-30-60 °C), promising a novel strategy to design advanced ABs positive electrodes with enhanced overall energy storage performance.