Dingding Ye

A three-dimensional nitrogen-doped graphene aerogel-activated carbon composite catalyst that enables low-cost microfluidic microbial fuel cells with superior performance

Microfluidic microbial fuel cells (μMFCs) are promising miniaturized power generators and bio-sensors, which combine the micro-fabrication process with bio-chip technology. However, a limited power output and considerable cost severely restrict their practical applications. Previous research has revealed that inadequate colonization of bacteria on bio-anodes as well as sluggish oxygen reduction reaction (ORR) kinetics are two main causes for the unsatisfactory power output. In this study, we have demonstrated a μMFC that has successfully addressed the aforementioned limitations by utilizing low-cost self-assembled reduced graphene oxide–nickel (rGO@Ni) foam and a nitrogen-doped graphene aerogel-activated carbon (AC@N-GA) as the bio-anode and air-cathode electrodes, respectively. The three-dimensional and macro-porous structure of the rGO@Ni foam provides a large surface area for bacterial colonization and hence largely increases the loading amount of bacterial cells. The AC@N-GA electrode shows excellent ORR catalytic performance due to the meso-porous structure and the presence of nitrogen functionalities that can serve as the catalytic sites. As a result, the μMFC achieves a maximum power density of 1181.4 ± 135.6 W m−3 (continuous-mode) and 690.2 ± 62.3 W m−3 (batch-mode) evaluated based on the volume of the reactor (50 μL). To our knowledge, this is the highest volumetric power density reported for air-breathing μMFCs and microfluidic glucose fuel cells with a similar configuration. Besides, the utilization of the inexpensive electrodes and membrane-free architecture could significantly decrease the fabrication cost of μMFCs.

Boosting Power Density of Microbial Fuel Cells with 3D Nitrogen-Doped Graphene Aerogel Electrode

A 3D nitrogen‐doped graphene aerogel (N‐GA) as an anode material for microbial fuel cells (MFCs) is reported. Electron microscopy images reveal that the N‐GA possesses hierarchical porous structure that allows efficient diffusion of both bacterial cells and electron mediators in the interior space of 3D electrode, and thus, the colonization of bacterial communities. Electrochemical impedance spectroscopic measurements further show that nitrogen doping considerably reduces the charge transfer resistance and internal resistance of GA, which helps to enhance the MFC power density. Importantly, the dual‐chamber milliliter‐scale MFC with N‐GA anode yields an outstanding volumetric power density of 225 ± 12 W m−3 normalized to the total volume of the anodic chamber (750 ± 40 W m−3 normalized to the volume of the anode). These power densities are the highest values report for milliliter‐scale MFCs with similar chamber size (25 mL) under the similar measurement conditions. The 3D N‐GA electrode shows great promise for improving the power generation of MFC devices.

Anolyte recirculation effects in buffered and unbuffered single-chamber air-cathode microbial fuel cells.

Two identical microbial fuel cells (MFCs) with a floating air-cathode were operated under either buffered (MFC-B) or bufferless (MFC-BL) conditions to investigate anolyte recirculation effects on enhancing proton transfer. With an external resistance of 50 Ω and recirculation rate of 1.0 ml/min, MFC-BL had a 27% lower voltage (9.7% lower maximal power density) but a 64% higher Coulombic efficiency (CE) than MFC-B. MFC-B had a decreased voltage output, batch time, and CE with increasing recirculation rate resulting from more oxygen transfer into the anode. However, increasing the recirculation rate within a low range significantly enhanced proton transfer in MFC-BL, resulting in a higher voltage output, a longer batch time, and a higher CE. A further increase in recirculation rate decreased the batch time and CE of MFC-BL due to excess oxygen transfer into anode outweighing the proton-transfer benefits. The unbuffered MFC had an optimal recirculation rate of 0.35 ml/min.

Increased performance of a tubular microbial fuel cell with a rotating carbon-brush anode

A novel method was proposed to improve the power output of microbial fuel cells (MFCs) by rotating the carbon-brush anode. The MFC with a rotating anode produced a peak power density of 210±3 W/m(3) and a maximum current density of 945±43 A/m(3), 1.4 and 2.7 times higher than those of the non-rotating case, respectively. The difference of the electrochemical impedance spectroscopy and cyclic voltammetry before and after anode rotation clearly suggested that the mass transfer to the spiral space was enhanced by the rotating anode. Furthermore, Tafel plots analysis also revealed that the rotating anode can improve the electrochemical activity of the biofilm.

Enhanced biofilm distribution and cell performance of microfluidic microbial fuel cells with multiple anolyte inlets.

A laminar-flow controlled microfluidic microbial fuel cell (MMFC) is considered as a promising approach to be a bio-electrochemical system (BES). But poor bacterial colonization and low power generation are two severe bottlenecks to restrict its development. In this study, we reported a MMFC with multiple anolyte inlets (MMFC-MI) to enhance the biofilm formation and promote the power density of MMFCs. Voltage profiles during the inoculation process demonstrated MMFC-MI had a faster start-up process than the conventional microfluidic microbial fuel cell with one inlet (MMFC-OI). Meanwhile, benefited from the periodical replenishment of boundary layer near the electrode, a more densely-packed bacterial aggregation was observed along the flow direction and also the substantially low internal resistance for MMFC-MI. Most importantly, the output power density of MMFC-MI was the highest value among the reported µl-scale MFCs to our best knowledge. The presented MMFC-MI appears promising for bio-chip technology and extends the scope of microfluidic energy.

Uneven biofilm and current distribution in three-dimensional macroporous anodes of bio-electrochemical systems composed of graphite electrode arrays

A 3-D macroporous anode was constructed using different numbers of graphite rod arrays in fixed-volume bio-electrochemical systems (BESs), and the current and biofilm distribution were investigated by dividing the 3-D anode into several subunits. In the fixed-volume chamber, current production was not significantly improved after the electrode number increased to 36. In the case of 100 electrodes, a significant uneven current distribution was found in the macroporous anode. This was attributed to a differential pH distribution, which resulted from proton accumulation inside the macroporous anode. The pH distribution influenced the biofilm development and led to an uneven biofilm distribution. With respect to current generation, the uneven distribution of both the pH and biofilm contributed to the uneven current distribution. The center had a low pH, which led to less biofilm and a lower contribution to the total current, limiting the performance of the BESs.

A laminar flow microfluidic fuel cell for detection of hexavalent chromium concentration

An electrochemical hexavalent chromium concentration sensor based on a microfluidic fuel cell is presented. The correlation between current density and chromium concentration is established in this report. Three related operation parameters are investigated, including pH values, temperature, and external resistance on the sensor performance. The results show that the current density increases with increasing temperature and the sensor produces a maximum regression coefficient at the catholyte pH value of 1.0. Moreover, it is found that the external resistance has a great influence on the linearity and current densities of the microfluidic sensor. Owing to the membraneless structure and the steady co-laminar flow inside the microchannel, the microfluidic sensor exhibits short response time to hexavalent chromium concentration. The laminar flow fuel cell sensor provides a new and simple method for detecting hexavalent chromium concentration in the industrial wastewater.

Experimental study on the durability of the polydopamine functionalized gas–liquid–solid microreactor for nitrobenzene hydrogenation

As a promising technique for multiphase catalytic reactions, the widespread applications of gas–liquid–solid microreactors are still limited by poor durability. Hence, in this work, a method for the preparation of Pd nanocatalysts inside a gas–liquid–solid microreactor was proposed to realize long-term durability using electroless deposition on the polydopamine functionalized surface followed by hydrogen reduction. This method not only increases the utilization efficiency of the Pd ions but also improves the durability of the microreactor. The chemical composition and topography characterization of the fabricated catalyst layer were tested using XPS and FESEM, respectively. The results indicated that the incorporation of hydrogen reduction resulted in nearly all palladium ions being reduced and the palladium nanoparticles were dispersed uniformly on the polydopamine modified surface. The microreactor prepared by this method exhibited high durability and high nitrobenzene conversion as compared to the traditional electroless catalyst deposition. Besides, it was shown that the increased inlet nitrobenzene concentration and flow rates played a negative role in the durability. The longer microreactor exhibited a better durability.

Electricity from Microbial Fuel Cells

Microbial fuel cells (MFCs) are a promising technology for treating wastewater and producing electricity using a diversity of inorganic/organic energy containing substrates. MFC performance has increased several orders of magnitude over the last decade and shows the potential for practical application. In this chapter, we review recent developments of MFC technology and provide an overview of the fundamental principles of MFCs, the electrode materials and their fabrication methods, and MFC architecture. We discuss the MFC stack and the feasibility of power generation, and we describe the various applications of MFC technology. Advances in highly efficient carbon materials used for electrodes have lowered the cost and improved the performance of MFCs. The construction of MFC stacks is a promising strategy for significantly enhancing power and current output. In addition, MFC-based biosensors for pollutant analysis and in situ process monitoring have widened the uses of MFC technology. Although high costs and low power output remain obstacles limiting its practical application, MFC technology is a carbon neutral technology that can be the foundation of a new generation of renewable energy systems.

A solar responsive photocatalytic fuel cell with the membrane electrode assembly design for simultaneous wastewater treatment and electricity generation

In this work, a photocatalytic fuel cell (PFC) with membrane electrode assembly (MEA) structure was designed for simultaneous organic compounds degradation and electricity generation. For the photoanode, the TiO2 with the quantum-dot sensitization by CdS-ZnS was used to broaden the absorption spectrum to visible light. For the cathode, an air-breathing mode was utilized to enhance the oxygen transport. The performance of the developed PFC was evaluated under different operation conditions, including the light intensity, liquid flow rate, concentrations of electrolyte and organics. Results indicated that the designed PFC could yield good performance. The increase of the light intensity and electrolyte concentration could improve the PFC performance. It is also found that when the flow rate was increased, the PFC performance dropped down in the testing range. Too high organics concentration led to the decrease of the PFC performance.