Ball-milled biochar for alternative carbon electrode.

Abstract

Ball-milled biochars (BM-biochars) were produced through ball milling of pristine biochars derived from different biomass at three pyrolysis temperatures (300, 450, and 600°C). The results of scanning electron microscopic (SEM), surface area, hydrodynamic diameter test, and Fourier transform infrared spectroscopy (FTIR) revealed that BM-biochars had smaller particle size (140-250nm compared to 0.5-1mm for unmilled biochar), greater stability, and more oxygen-containing functional groups (2.2-4.4mmol/g compared to 0.8-2.9 for unmilled biochar) than the pristine biochars. With these changes, all the BM-biochar-modified glassy carbon electrodes (BM-biochar/GCEs) exhibited prominent electrochemical properties (e.g., ΔEp of 119-254mV compared to 850mV for bare GCE). Cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) show that ball-milled 600°C biochar/GCE (BMBB600/GCE and BMBG600/GCE) had the smallest peak-to-peak separation (ΔEp= 119 and 132mV, respectively), series resistance (RS= 88.7 and 89.5Ω, respectively), and charge transfer resistance (RCT= 1224 and 1382Ω, respectively), implying its best electrocatalytic activity for the reduction of Fe(CN)63-. It is supposed that the special structure (i.e., internal surface area, pore volume, oxygen-containing functional groups, and graphitic structure) facilitates the electron transfer and reduces interface resistance. Economic cost of BM-biochar/GCE was 1.97 × 10-7 USD/cm2, much lower than that of a "low-cost platinum electrode" (0.03 USD/cm2). The results indicate potential application of the novel BM-biochar for low cost and high efficient electrodes. Graphical abstract.