Electrochemical Activity Of Hydrolysate

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Gold electrodes were prepared after cleaning with H2SO4 and H2O2. Glucose oxidase and laccase were immobilized on the GO/Co/chitosan modified electrodes in a sodium phosphate buffer solution (0.1 M, Ph 7) for 8 h [12]. The electrochemical activities of enzymatic electrodes were measured using VersaSTAT3 (AMETEK, Princeton Applied Research, USA). Electrochemical measurements such as CV and EIS were carried out using an Au electrode with the assembled glucose oxidase, Ag/AgCl, and a Pt wire as the working electrode, reference electrode, and the counter electrodes, respectively [13]. The following parameters were used to measure EIS using a Nyquist plot: start frequency, 20 Hz; end frequency, was 0.01 Hz; and amplitude voltage, 10 mV. The resistances …show more content…
3. Results
3.1 Cyclic voltammetry measurement
CV of the redox reaction of the hydrolysate was measured at various concentrations. In the 80 °C bath, the initial hydrolysate concentration was 2% and was further diluted to 1% and 0.5%. Fig. 2(A) shows the CV curves, indicating the tendency and relation of current with varying potential (volt). As the hydrolysate dilution was increased, the maximum current density decreased. CV is widely used to obtain the voltammetry data. The cyclic voltamograms provides the information of the redox reaction and adsorption/desorption effects with the applied potential. In addition, the stability, reversibility, and electron transfer kinetics can be determined using the CV peak behavior. CV can also be used to determine the electron stoichiometry of a system, the diffusion coefficient of an analyte, and the formal reduction potential of an analyte as an identification tool [13]. The CV was measured at a scan rate of 100 mV/s between –0.6 V to +0.6 V. The CV results showed the irreversible curves of the reduction reaction using electrons from the glucose oxidation reaction governed by Laccase. No inverse peak was observed as
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Fig. 2(B) shows the Nyquist plot of the EIS of the EFC system using the hydrolysate. The results of the EIS for the hydrolysates showed a similar tendency of impedance. The semicircle portion at high frequency and linear portion (Warburg impedance) at a low frequency were observed. The resistance of charge-transfer (Rct) and the electrolyte resistance (Rs) could be calculated using the diameter of the semicircle in the plot and the intercept on the real axis of the semicircle [18]. At 2, 1, and 0.5% glucose samples of the EFC system, the Rct values were found to be 5.4, 3.5, and 3.9k Ω, respectively. Some properties of hydrolysate affect the charge-transfer on the electrode surface. The electrodes were modified by assembling GO/Co/chitosan composites and redox enzymes on the surface for power generation. Then, Rct is affected by both the property of electrode and modification of the electrode surface [19]. The enzyme loading on the electrode surface could be verified by comparison of the Rct values [20]. Because the identical sets of electrodes were used for the EIS measurements, hydrolysate is the strong influential factor towards the charge transfer. The hydrolysate liquid after the DAP of lignocellulosic biomass involves various undefined materials derived from the biomass by hydrolysis and pyrolysis.

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