Sodium-ion batteries (SIBs) serve as the most promising next-generation commercial batteries besides lithium-ion batteries (LIBs). Hard carbon (HC) from renewable biomass resources is the most commonly used anode material in SIBs. In this contribution, we present a review of the latest progress in the conversion of waste biomass to HC materials, and highlight their application in SIBs. Specifically, the following topics are discussed in the review: (1) the mechanism of sodium-ion storage in HC, (2) the HC precursor’s sources, (3) the processing methods and conditions of the HCs production, (4) the impact of the biomass types and carbonization temperature on the carbon structure, and (5) the effect of various carbon structures on electrochemical performance. Data from various publications have been analyzed to uncover the relationship between the processing conditions of biomass and the resulting structure of the final HC product, as well as its electrochemical performance. Our results indicate the existence of an ideal temperature range (around 1200 to 1400 °C) that enhances the formation of graphitic domains in the final HC anode and reduces the formation of open pores from the biomass precursor. This results in HC anodes with high storage capacity (>300 mAh/g) and high initial coulombic efficiency (ICE) (>80%).

The iron and steelmaking industry faces the dilemma of the need to decrease their greenhouse gas emissions to align with decarbonization goals, while at the same time fulfill the increasing steel demand from the growing population. Replacing fossil coal and coke with biomass-based carbon materials reduces the net carbon dioxide emissions. However, there is currently a shortage of charcoal to fully cover the demand from the iron and steelmaking industry to achieve the emission-reduction goals. Moreover, the transportation and energy sectors can compete for biofuel usage in the next few decades. Simultaneously, our society faces challenges of accumulation of wastes, especially wet organic wastes that are currently not reused and recycled to their full potentials. Here, hydrothermal carbonization is a technology which can convert organic feedstocks with high moisture contents to solid fuels (hydrochar, one type of biochar) as an alternative renewable carbon material. This work studied the differences between a hydrochar, produced from lemon peels (Lemon Hydrochar), and two types of charcoals (with and without densification) and an Anthracite coal. Characterizations such as chemical and ash compositions, thermogravimetric analyses in nitrogen and carbon dioxide atmospheres, scanning electron microscope analyses of carbon surface morphologies, and pyrolysis up to 1200 °C were performed. The main conclusions from this study are the following: (1) hydrochar has a lower thermal stability and a higher reactivity compared to charcoal and Anthracite; (2) densification resulted in a reduction of the moisture pickup and CO₂ reactivity of charcoal; (3) pyrolysis of Lemon Hydrochar resulted in the formation of a large amount of tar (17 wt%) and gas (39 wt%), leading to its low fixed carbon content (27 wt%); (4) a pyrolyzed hydrochar (up to 1200 °C) has a comparable higher heating value to those of charcoal and Anthracite, but its phosphorous, ash, and alkalis contents increased significantly; (5) based on the preliminary assessment, hydrochar should be blended with charcoal or Anthracite, or be upgraded through slow pyrolysis to fulfill the basic functions of carbon in the high-temperature metallurgical processes.

Effective bromine mitigation is a critical challenge in the sustainable recycling of electronic waste, where the uncontrolled release of brominated species compromises both environmental safety and product quality. This study unveils a novel synergistic transformation pathway of bromine (Br) during ex situ dual-catalyst pyrolysis of waste electronic circuit boards (WECBs). Experiments were conducted in a continuous auger reactor integrated with a fixed-bed catalytic unit employing a dual (HZSM-5/CaO) catalyst system. By tuning the weight hour space velocity WHSV from 0.6 to 1.0 h^–1, the catalytic process not only doubled the gas yield from 2.7 to 6.5 wt % but also selectively suppressed liquid formation from 18.0 to 12.5 wt %, while driving deeper deoxygenation and aromatic hydrocarbon enrichment. At lower WHSV, intensified secondary reactions promoted the generation of lighter aromatics and also accelerated coke deposition, highlighting the need for WHSV optimization. Mechanistic insights reveal that brominated phenols and aromatic hydrocarbons dominate the primary volatile fraction, where Br⁺ radicals undergo dual pathways: recombination with H⁺ and small fragments forming HBr/CH₃Br, or neutralization by CaO to yield stable CaBr₂. Importantly, 44 wt % of total bromine was retained in the solid residue as CaBr₂, drastically lowering bromine content in pyrolysis oils. The dual-catalyst strategy thus enables simultaneous Br-fixation, hydrocarbon upgrading, and catalyst regeneration, drastically reducing bromine in pyrolysis oils. These findings provide a scalable, mechanistically guided route for the valorization of cleaner electronic waste, coupling environmental protection with high-value fuel production.