Rational Design of Single-Atom Site Electrocatalysts: From Theoretical Understandings to Practical Applications

Atomically dispersed metal-based electrocatalysts have attracted increasing attention due to their nearly 100% atomic utilization and excellent catalytic performance. However, current fundamental comprehension and summaries to reveal the underlying relationship between single-atom site electrocatalysts (SACs) and corresponding catalytic application are rarely reported. Herein, the fundamental understandings and intrinsic mechanisms underlying SACs and corresponding electrocatalytic applications are systemically summarized. Different preparation strategies are presented to reveal the synthetic strategies with engineering the well-defined SACs on the basis of theoretical principle (size effect, metal-support interactions, electronic structure effect, and coordination environment effect). Then, an overview of the electrocatalytic applications is presented, including oxygen reduction reaction, hydrogen evolution reaction, oxygen evolution reaction, oxidation of small organic molecules, carbon dioxide reduction reaction, and nitrogen reduction reaction. The underlying structure-performance relationship between SACs and electrocatalytic reactions is also discussed in depth to expound the enhancement mechanisms. Finally, a summary is provided and a perspective supplied to demonstrate the current challenges and opportunities for rational designing, synthesizing, and modulating the advanced SACs toward electrocatalytic reactions.

A Critical View of Microbial Fuel Cells: What Is the Next Stage?

Microbial fuel cells (MFCs) have garnered interest from the scientific community since the beginning of this century and this has caused a considerable increase in the scientific production of MFCs. However, the ability of MFCs to generate power has not increased considerably within this timeframe. In recent years, the power generated by MFCs has remained at an almost contact level owing to difficulties in the scale-up of the technology and thus the application of MFCs for powering systems with high energy demands will not be fully developed, at least within a short temporal horizon. Scale-up by increasing the size of the electrodes has failed, because of the wrong assumption that a linear function describes the relationship between the amount of power generated by a MFC and its size. However, more efficient energy generation upon working with small MFCs has been described. This has led to a new approach for scaling up on the basis of miniaturization and replication. Then, MFCs can be connected electrically in series to increase the overall potential and in parallel to increase the overall current. However, cell-voltage reversal and ionic short-circuit issues must be solved for this approach to be successful. Nowadays, the applicability of MFC technology in wastewater treatment does not make any sense in light of the power levels reached, despite the fact that MFCs were seen as a paramount opportunity less than a decade ago. However, MFCs can be used for wastewater treatment with coupled energy generation, as well as for other technologies such as biosensors and biologically inspired robots.

Effects of Fe, Ni, and Fe/Ni metallic nanoparticles on power production and biosurfactant production from used vegetable oil in the anode chamber of a microbial fuel cell

In this study, metallic nanoparticles (Fe, Ni, and Fe/Ni) were used as cathode catalysts to enhance power production and to improve the anode performance of a two-chambered microbial fuel cell (MFC). The metallic nanoparticles were rod-shaped and produced by the precipitation/co-precipitation method. A biosurfactant was produced in the anode chamber of the MFC from used vegetable oil by the bacteria Serratia sp. Overall cell voltage, power density, bacterial growth, and biosurfactant production were studied by applying different types of metallic nanoparticles to the cathode electrode. The influence of various types of nanoparticles on the impedance of the MFC was also investigated by electrochemical impedance spectroscopy (EIS), including analyses of anode impedance, cathode impedance, anode solution resistance, cathode solution resistance, and membrane resistance. The nanoparticles improved MFC performance in the following order: Fe>Ni>Fe/Ni. The addition of 1.5mg/cm² Fe nanoparticles to the cathode surface enhanced power production by over 500% to 66.4mW/m³, promoted bacterial growth and biosurfactant production in the anode solution by 132.5% and 32.0%, respectively, and reduced anode impedance, cathode impedance, and membrane resistance by 26.8%, 81.6%, and 33.8% to 159.00Ω, 7.69Ω, and 261.09Ω, respectively. For the first time, biosurfacant production in the anode chamber of the MFC was promoted by using the metallic nanoparticles as cathode catalysts. By improving the cathode properties, this study showed a new way to manipulated the performance of the anode chamber of the MFC.

Enhanced bioelectricity generation of double-chamber air-cathode catalyst free microbial fuel cells with the addition of non-consumptive vanadium(v)

Improvement of microbial fuel cells (MFCs) via bioelectricity recovery is urgently needed in micro-energy devices nowadays.

Using live algae at the anode of a microbial fuel cell to generate electricity

Live green microalgae Chlorella pyrenoidosa was introduced in the anode of a microbial fuel cell (MFC) to act as an electron donor. By controlling the oxygen content, light intensity, and algal cell density at the anode, microalgae would generate electricity without requiring externally added substrates. Two models of algal microbial fuel cells (MFCs) were constructed with graphite/carbon electrodes and no mediator. Model 1 algal MFC has live microalgae grown at the anode and potassium ferricyanide at the cathode, while model 2 algal MFC had live microalgae in both the anode and cathode in different growth conditions. Results indicated that a higher current produced in model 1 algal MFC was obtained at low light intensity of 2500 lx and algal cell density of 5 × 10(6) cells/ml, in which high algal density would limit the electricity generation, probably by increasing oxygen level and mass transfer problem. The maximum power density per unit anode volume obtained in model 1 algal MFC was relatively high at 6030 mW/m(2), while the maximum power density at 30.15 mW/m(2) was comparable with that of previous reported bacteria-driven MFC with graphite/carbon electrodes. A much smaller power density at 2.5 mW/m(2) was observed in model 2 algal MFC. Increasing the algal cell permeability by 4-nitroaniline would increase the open circuit voltage, while the mitochondrial acting and proton leak promoting agents resveratrol and 2,4-dinitrophenol would increase the electric current production in algal MFC.