Extensive efforts have been devoted to improve the anode performance of a microbial fuel cell (MFC) by using modified carbon-based anode materials, but most of them did not recognize that the power performance measured by the commonly-used varying circuit resistance (VCR) or linear sweep voltammetry (LSV) method was overestimated due to the effect of anode capacitance. Here, we examined and compared the transient power and the stationary power of a series of MFCs equipped with the polypyrrole-graphene oxide (PPy-GO)-modified graphite felt anodes. It was found that noticeable transient power was recorded when the VCR or LSV method was chosen for power measurements. Calculations on the contribution of different sources to the measured maximum power density showed that the discharge of bio-electrons stored in the high-capacitance anode was a dominant contributor, especially when the time duration (for the VCR method) was not sufficiently long or the scan rate (for the LSV method) was not sufficiently low. Although anode modification with capacitive materials can result in the increased stationary power obtained from the fed-batch cycle test, owing to the increases in the anode surface area and the number of bacteria attached to anode, the increase in the transient power was more remarkable.

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In this study, a novel method, termed dielectric-barrier-discharge-plasma (DBDP) assisted ball milling and low-temperature carburization, was used to synthesize WC-Co nanocomposite powder. X-ray diffraction, scanning/transmission electron microscopy, and differential scanning calorimetry were used to characterize the microstructure of powders. Starting from W, Co, and graphite powder mixtures, the DBDP-milled W-C-10Co powder exhibited a flakelike morphology with very fine lamellar structure. The WC-Co composite powder was synthesized at 1273 K (1000°C), which is much lower than the requisite temperature for the conventional carburizing method. The obtained WC-Co composite powder had a nanocomposite microstructure in which fine WC particles were bounded by homogenously distributed Co phase, and the WC crystals had a slablike morphology with a planar size of about 200 nm and <100-nm thickness. The combinational effect of the milling and the plasma in the DBDP milling caused a unique fine flakelike morphology and high-density interfaces in the W-C-10Co powder mixture, which is responsible for the reduced carburization temperature and the nanocomposite structure of WC-Co powder.

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