Evaluation of four preparation methods and electrochemical properties of walnut shell-based activated carbon

This study proposes four biomass-based activated carbon (AC) preparation methods to evaluate the effects of preparation processes (one/two-step process), heating rate, and carbonization temperature on the product yield, as well as on the structural properties and electrochemical performance of AC. The results reveal that the one-step process, a high heating rate, and an appropriate carbonization temperature help to produce AC with a large specific surface area (SSA) and good electrochemical performance. However, these conditions may result in a partial loss of AC yield. Among the four preparation methods, the one-step process (M1) — fast pyrolysis at 650 °C with in-situ activation at 700 °C for 2 h — achieved AC with an SSA of 744.8 m² g⁻¹, the highest specific capacitance of 265.62 F g⁻¹ at 0.5 A g⁻¹, and a capacitance retention rate of 93.41 % after 5000 cycles at 2 A g⁻¹. The first comparison of the economics of different methods was conducted, and the results further revealed that M1 is the optimal process due to its lowest consumption of time, energy, and raw materials, along with the minimum comprehensive cost index, when preparing electrode materials with equivalent capacitance. This method provides a novel and efficient strategy for advancing biomass processing technologies.