Using the self-templating structure of rice husk (RH), hierarchical porous carbon with high surface area was prepared by carbonization, NaOH-leaching and KOH activation. The formation processes of the hierarchical porous structure were discussed in detail, where the silica in RH plays a crucial role. The rice husk-based hierarchical porous carbon (RHHPC) with a 3D porous structure, was composed of macrochannels, mesopores and micropores both on its surface and inner channels. The RHHPC exhibited a surface area as high as 2804 m² g⁻¹ and a high-level of oxygen-containing groups (with an oxygen content of 9.74 at%). The high surface area, large amount of oxygen-containing groups and unique hierarchical porous structure endow the RHHPC with a high capacitance (278 F g⁻¹ at 0.5 A g⁻¹) and excellent rate capability (77.2% retention at 20 A g⁻¹) in 6 mol L⁻¹ KOH. Furthermore, the symmetric supercapacitor fabricated with RHHPC delivered a high energy density of 7.4 W h kg⁻¹ at a power density of 6195 W kg⁻¹, which reveals the promising application of RHHPC in high-performance supercapacitors.

The lead acid battery has been a dominant device in large-scale energy storage systems since its invention in 1859. It has been the most successful commercialized aqueous electrochemical energy storage system ever since. In addition, this type of battery has witnessed the emergence and development of modern electricity-powered society. Nevertheless, lead acid batteries have technologically evolved since their invention. Over the past two decades, engineers and scientists have been exploring the applications of lead acid batteries in emerging devices such as hybrid electric vehicles and renewable energy storage; these applications necessitate operation under partial state of charge. Considerable endeavors have been devoted to the development of advanced carbon-enhanced lead acid battery (i.e., lead-carbon battery) technologies. Achievements have been made in developing advanced lead-carbon negative electrodes. Additionally, there has been significant progress in developing commercially available lead-carbon battery products. Therefore, exploring a durable, long-life, corrosion-resistive lead dioxide positive electrode is of significance. In this review, the possible design strategies for advanced maintenance-free lead-carbon batteries and new rechargeable battery configurations based on lead acid battery technology are critically reviewed. Moreover, a synopsis of the lead-carbon battery is provided from the mechanism, additive manufacturing, electrode fabrication, and full cell evaluation to practical applications. Graphical abstract

Bi-functional electrode materials, composed of capacitive activated carbon (AC) and battery electrode materials, possess higher power performance than traditional battery electrode materials. Negative electrodes of lead acid batteries with AC additives (i.e., lead–carbon electrodes) display much better charge acceptance than do traditional lead negative electrodes, and are suitable for energy storage in hybrid electrical vehicles. In this paper, we discuss the electrochemical processes on AC in lead–carbon electrodes. In the charging process of the lead–carbon electrode, lead electrodeposits on AC at potentials higher than the open circuit potential of lead, and the large surface area of AC provides extra active sites for lead electrodeposition and the growth of the electrochemical active surface area of lead. Namely, AC acts as an electron bumper and electron distributor in the charging process of the lead–carbon electrode. Most importantly, at high charge rates, the hydrogen evolution reaction (HER) on AC is prohibited by reversible hydrogen adsorption; and meanwhile the adsorbed hydrogen contributes to the charging process.