Search

Abstract High-efficiency cathode catalysts are essential for microbial fuel cell development since they are one of the key components in chemical energy conversion in organic compounds into electricity. Here, novel Fe Mn bimetallic nanocatalysts are designed and hydrothermally synthesized for microbial fuel cells. Fe:Mn (atom%) = 1:4, 1:2, 1:1, and α-MnO 2 are applied in air-cathodes with Pt/C and activated carbon catalysts as benchmarks, and Fe Mn catalysts can enhance the performance. When Fe:Mn = 1:2, the FeMn 2 achieves a maximum power density of 1940 ± 31 mW m−2 in microbial fuel cells and a current density of 19.4 A m−2 at −0.056 V in abiotic electrochemical tests, 24% and 37% higher than Pt/C respectively. Material characteristics are systematically analyzed since they are directly related to the catalytic performance. The high catalytic activity of FeMn 2 proves to result from a combination of the weak Mn O bonds, large quantity of defects, large specific surface area and high Mn(III):Mn(IV) ratio, according to the proposed possible mechanisms of Fe Mn catalysts to enhance the output. This work not only puts forwards an easy-to-accomplish method to design and prepare bimetallic nanocatalysts, but also provides a potential alternative to Pt/C in microbial fuel cells for sustainable energy generation. Graphical abstract Image 1 Highlights • Fe Mn nanocatalysts were designed and prepared for MFC via hydrothermal method. • FeMn 2 air-cathode exhibited the highest MFC maximum power density of 1940 mW m−2. • The synergism of Fe3+ and α-MnO 2 lattice has been demonstrated. • The best performance of FeMn 2 was illustrated by proposed catalytic mechanisms. • The FeMn 2 outperformed commercial Pt/C and could be a potential alternative. [ABSTRACT FROM AUTHOR]

[Display omitted] • BCFZY and Ni doped BCFZY cathodes are synthetized. • Ni doped BCFZY improves the oxygen ion and proton conductivity of the cathode. • BCFZYN has a good thermal stability and a reduced thermal expansion coefficient. • Ni doping enhances the ORR activity in both O-SOFCs and PCFCs. • BCFZYN exhibits a prominent stability in both symmetrical cell and single cell test. To develop a cathode with excellent oxygen reduction reaction (ORR) activity and durability at intermediate-to-low temperatures is significant to boost the advancement of solid oxide fuel cells (SOFCs), a fascinating energy conversion technology with low emissions and high efficiency. Perovskite oxides have been extensively developed as cathodes, and doping is an important strategy to alter the lattice diffusion and surface exchange properties of perovskites, to tailor catalytic performances for various redox reactions, including ORR for SOFCs. The reported BaCo 0.4 Fe 0.4 Zr 0.1 Y 0.1 O 3-δ (BCFZY) is a promising cathode for SOFCs. Herein, to further improve the performance of BCFZY at reduced temperatures, we systematically investigate the partial doping of B-sites with different metal elements, including Mn, Ni, Cu and Zn at a fixed content of 5%. Among them, it is found that Ba(Co 0.4 Fe 0.4 Zr 0.1 Y 0.1) 0.95 Ni 0.05 O 3-δ (BCFZYN) exhibits the lowest polarization impedance in both oxygen ion and proton conducting fuel cells. Based on conductivity relaxation experiments and oxygen and hydrogen permeation tests, it is found that nickel doping improves oxygen mobility, surface exchange kinetics, and bulk oxygen ion and proton conductivity. Thereby, a high ORR activity on oxygen ion and proton conducting electrolytes is achieved, reaching 0.038 and 0.607 Ω cm2 at 550 °C, respectively. The cells with the BCFZYN electrode show outstanding operational stability (200 h of operation in a symmetrical cell and 1000 h of operation in a single cell). This suggests that the BCFZYN is a promising cathode of next-generation SOFCs. [ABSTRACT FROM AUTHOR]

Direct urea fuel cells (DUFCs) have recently drawn increased attention as sustainable power generation devices because of their considerable advantages. Nonetheless, the kinetics of the oxidation-reduction reaction, particularly the electrochemical oxidation and oxygen reduction reaction (ORR), in direct urea fuel cells are slow and hence considered to be inefficient. To overcome these disadvantages in DUFCs, Pd nanoparticles loaded onto Co3O4 supported by multi-walled carbon nanotubes (Pd/Co3O4@MWCNT) were employed as a promising cathode catalyst for enhancing the electrocatalytic activity and oxygen reduction reaction at the cathode in DUFCs. Co3O4@MWCNT and Pd/Co3O4@MWCNT were synthesized via a facile two-step hydrothermal process. A Pd/MWCNT catalyst was also prepared and evaluated to study the effect of Co3O4 on the performance of the Pd/Co3O4@MWCNT catalyst. A current density of 13.963 mA cm−2 and a maximum power density of 2.792 mW cm−2 at 20 °C were obtained. Pd/Co3O4@MWCNT is a prospectively effective cathode catalyst for DUFCs. The dilution of Pd with non-precious metal oxides in adequate amounts is economically conducive to highly practical catalysts with promising electrocatalytic activity in fuel cell applications. [ABSTRACT FROM AUTHOR]

The construction of optimized biological fuel cells requires a cathode which combines the longevity of a microbial catalyst with the current density of an enzymatic catalyst. Laccase-secreting fungi were grown directly on the cathode of a biological fuel cell to facilitate the exchange of inactive enzymes with active enzymes, with the goal of extending the lifetime of laccase cathodes. Directly incorporating the laccase-producing fungus at the cathode extends the operational lifetime of laccase cathodes while eliminating the need for frequent replenishment of the electrolyte. The hybrid microbial–enzymatic cathode addresses the issue of enzyme inactivation by using the natural ability of fungi to exchange inactive laccases at the cathode with active laccases. Finally, enzyme adsorption was increased through the use of a functionally graded coating containing an optimized ratio of titanium dioxide nanoparticles and single-walled carbon nanotubes. The hybrid microbial–enzymatic fuel cell combines the higher current density of enzymatic fuel cells with the longevity of microbial fuel cells, and demonstrates the feasibility of a self-regenerating fuel cell in which inactive laccases are continuously exchanged with active laccases. [ABSTRACT FROM AUTHOR]

Designing affordable high efficient oxygen reaction (ORR/OER) electrocatalyst is a major task for promoting sustainable energy conversion batteries (such as Zn-air batteries and fuel cells). Herein, a bifunctional oxygen reaction electrocatalyst with excellent activity and stability constructed using the peasecod-like N-doped carbon nanotubes (N/CNT) in situ confinement encapsulate bimetallic FeCu alloy (FeCu–N/C). The bimetallic FeCu alloy embedded into N/CNT that inhibits serious polymerization of copper, increases Fe/Cu–N bimetallic active sites, improves conductivity, reduces the energy barrier of oxygen reaction and speeds up reaction kinetics, thus obtaining efficient ORR/OER performance. The optimal FeCu–N/C electrocatalyst reveal more positive half-wave potential for ORR, smaller overpotential for OER and lower ORR/OER potential gap than those of commercial grade Pt/C, IrO 2 and many reported catalysts. Moreover, the zinc-air batteries constructed using FeCu–N/C as the air electrode indicate the high power density and excellent stability. The alkaline anion exchange membrane fuel cells assembled with FeCu–N/C as cathode also exhibit enhanced power density compared to single metal-based catalysts (Fe–N/C and Cu–N/C). This work demonstrates potential use of FeCu–N/C for energy conversion and storage applications, provides a new sight for the reasonable design of bifunctional oxygen reaction electrocatalysts. Image 1 • A bifunctional oxygen reaction catalyst constructed using FeCu alloy encapsulated in peasecod-like N-rich carbon nanotubes. • The FeCu alloy increases Fe/Cu-N bimetallic active sites, conductivity and electrocatalytic oxygen reaction activity. • The FeCu 0.3 -N/C exhibited the low ORR/OER potential gap (△ E) of 0.777 V and extraordinary stability. • The FeCu 0.3 -N/C reveals superb cathode catalytic activity in zinc-air batteries and anion exchange membrane fuel cells. [ABSTRACT FROM AUTHOR]