Electrocatalytic potentials of biochars derived from Dioscorea bulbifera peel for hydrogen evolution reactions-...

This study reports the electrocatalytic characteristics of biochars prepared from Dioscorea bulbifera seed peel for hydrogen evolution reactions (HERs) through the electrochemical and tight binding quantum chemical study. The biochars obtained through pyrolysis at 300 °C and 400 °C, were subjected to chemical activation to obtained DBP@BC_300 and DBP@BC_400 respectively. The physicochemical properties of the activated biochars was evaluated using FTIR spectroscopic and BET surface area measurements. The electrocatalytic performance were evaluated using double layer capacitance values (C_DL) from cyclic voltammetry (CV), Tafel slopes from linear sweep voltammetry (LSV) and charge transfer resistance (R_CT) from electrochemical impedance spectroscopy (EIS) in different pH media. GFN2-xTB computational technique was adopted to determine the energy gap (ΔE) and Fermi energy level values of the proposed biochar models. The biochar derived electrocatalysts studied showed varying degrees of electrocatalytic performance in acidic, alkaline and neutral electrolyte solutions. DBP@BC_300 °C gave C_DL values of 2.6 mF, 2.7 mF and 2.8 mF in acidic, alkaline and neutral pH respectively and DBP@BC_400 °C gave C_DL values of 5.5 mF, 4.5 mF and 4.0 mF in alkaline, neutral and acidic pH respectively. These suggest that DBP@BC_400 gave the best electrocatalytic performance for HER in alkaline pH. The CV derived results are in excellent agreement with EIS with charge transfer resistance (R_CT) value of 90.00 Ω also in alkaline pH. Strong negative correlations were determined between Fermi energy and C_DL, R² = 0.968 and 0.7185 respectively for DBP@BC_300 and DBP@BC_400. GFN2-xTB calculations reveals that the DOS curves close to the Fermi energy level are not zero for both studied electrocatalyst biochar materials. This indicates the presence of electronic states available at the Fermi energy level, which enhanced easy charge transfers during hydrogen evolution reactions, and better electrocatalytic performance. Our results show that DBP@BC_400 has better hydrogen evolution reaction electrocatalytic property than DBP@BC_300.