Glucose/O 2 Enzymatic Biofuel Cell Constructed with a Laccase-Mimicking Nanozyme for Efficient Cathode Oxygen Reduction and Bacterial Surface-Displayed Cascade Enzymes for an Anode Biocatalyst

Enzymatic biofuel cell (EBFC) is an electrochemical device that uses enzymes to convert the chemical energy of renewable biomass into electrical energy. However, improving the EBFC performance, such as the cost-effectiveness, operational stability, output power density (Pmax), and open circuit voltage (OCV), remains challenging. Especially, the activity and stability of enzymes, substrate tolerance, cost, and immobilization strategy are crucial in developing EBFCs. Herein, we report on MnO2 nanosheets (MnO2 NSs) prepared via facile chemical precipitation, exhibiting outstanding laccase-mimicking activity with good stability and excellent resistance to halide ions. Then, for the first time, the laccase-like nanozyme could replace natural laccase as a cathode catalyst for efficient oxygen reduction reaction under nearly neutral pH condition, which exhibits an onset potential of 841 mV vs NHE in O2 reduction mediated by 2,2-bisazo-bis(3-ethyl-benzothiazole-6-sulfonic acid) diammonium salt. In addition, cascade enzymes of polyphosphate glucokinase (PPGK) and glucose 6-phosphate dehydrogenase (G6PDH) were successfully displayed on the Escherichia coli (E. coli) surface. The resultant PPGK-E. coli can catalyze the oxidation of glucose to glucose-6-phosphate (G6P), which can be subsequently oxidized by G6PDH-E. coli in the presence of the coenzyme NAD+ efficiently and converted to NADH. Finally, a dual-chamber glucose/O2 EBFC was constructed with PPGK-E. coli/G6PDH-E. coli (2:1) as the anodic catalyst and an MnO2 NS-based cathodic catalyst. The bacterial surface-displayed enzymes were kept in an anodic solution, which could not only retain the enzyme activity but also ensure mass transfer efficiency, thereby greatly enhancing the enzyme's inherent catalytic potential. The as-developed EBFC achieved an OCV of 0.68 V and a Pmax of 32.2 μW/cm2 as well as good operational stability. The strategies proposed provide new ideas for constructing high-performance EBFCs using other nanozymes and biocatalysts, which may provide new avenues for the development and utilization of sustainable energy for promising applications in wearable devices or in self-powered sensors.