Efficient Conversion of Lignin to Electricity Using a Novel Direct Biomass Fuel Cell Mediated by Polyoxometalates at Low Temperatures

Abstract

A novel polyoxometalates (POMs) mediated direct biomass fuel cell (DBFC) was used in this study to directly convert lignin to electricity at low temperatures with high power output and Faradaic efficiency. When phosphomolybdic acid H3 PMo12 O40 (PMo12) was used as the electron and proton carrier in the anode solution with a carbon electrode, and O2 was directly used as the final electron acceptor under the catalysis of Pt, the peak power density reached 0.96 mW cm(-2), 560 times higher than that of phenol-fueled microbial fuel cells (MFCs). When the cathode reaction was catalyzed by PMo12, the power density could be greatly enhanced to 5 mW cm(-2). Continuous operation demonstrated that this novel fuel cell was promising as a stable electrochemical power source. Structure analysis of the lignin indicated that the hydroxyl group content was reduced whereas the carbonyl group content increased. Both condensation and depolymerization takes place during the PMo12 oxidation of lignin.

Polyoxometalate‐Mediated Lignin Oxidation for Efficient Enzymatic Production of Sugars and Generation of Electricity from Lignocellulosic Biomass

“…developed a solar‐induced hybrid fuel cell that can be directly powered with natural polymeric biomasses, such as starch, using polyoxometalates as a photocatalyst and charge carrier to generate electricity at low temperatures . In our previous work, we also achieved efficient conversion of lignin to electricity at 90 °C with an output power density in the range of 0.3–45 mW cm −2 , depending on the oxidant used in the cathode . However, when air or oxygen is directly used as the oxidant for discharging, a noble metal catalyst such as Pt has to be used to facilitate the cathodic reaction, and the power density is relatively low.…”

“…However, when air or oxygen is directly used as the oxidant for discharging, a noble metal catalyst such as Pt has to be used to facilitate the cathodic reaction, and the power density is relatively low. Liquid catalysts such as POMs have been used as the electron mediator in the cathode, which greatly improved the power output . However, POMs are relatively expensive, and furthermore, most reduced POMs are not steadily and easily re‐oxidized by air under mild conditions.…”

“…Herein, we have proposed an integrated process mediated by POMs for biomass pretreatment to increase the cellulose digestibility coupled with efficient conversion of the biomass component (especially lignin) to electricity at low temperatures by using a liquid flow cell; this is effectively the conceptual integration of biomass pretreatment coupled with electricity generation (BPCEG, Figure B). This conceptual integration can be considered as a modified and updated version of the direct biomass‐to‐electricity conversion technology with POMs as electron mediators reported recently . The cell consisted of an anode chamber and cathode chamber separated by a proton exchange membrane (PEM).…”

“…The substrate surface became much coarser with porous structure (Figure 2 B), and therefore the specific surface area was greatly increased; spherical particles were also observed. It was observed that PMo 12 oxidation may cause acid‐catalyzed condensation of lignin to lead to higher molecular weight . Therefore, the spherical particles were probably produced by condensation of lignin and its re‐precipitation on the fiber surface.…”

“…The typical cathode used for proton exchange membrane fuel cells (PEMFCs) is made of carbon paper with gas diffusion layers and covered with Pt catalyst. However, this cathode does not yet obtain a high power density (<1 mW cm −2 ) for direct biomass fuel cells . The discharging efficiency could be improved greatly by using liquid catalysts or oxidants, and POM also has been found to be good electron mediator for the cathode to transfer an electron to oxygen .…”