Steam activation of Fe-N-C catalyst for advanced power performance of alkaline hydrazine fuel cells

Alkaline hydrazine liquid fuel cells(AHFC) have been highlighted in terms of high power performance with non-precious metal catalysts.Although Fe-N-C is a promising non-Pt electrocatalyst for oxygen reduction reaction(ORR),the surface density of the active site is very low and the catalyst layer should be thick to acquire the necessary number of catalytic active sites.With this thick catalyst layer,it is important to have an optimum pore structure for effective reactant conveyance to active sites and an interface structure for faster charge transfer.Herein,we prepare a Fe-N-C catalyst with magnetite particles and hierarchical pore structure by steam activation.The steam activation process significantly improves the power performance of the AHFC as indicated by the lower IR and activation voltage losses.Based on a systematic characterization,we found that hierarchical pore structures improve the catalyst utilization efficiency of the AHFCs,and magnetite nanoparticles act as surface modifiers to reduce the interracial resistance between the electrode and the ion-exchange membrane.

Optimistic performance of carbon-free hydrazine fuel cells based on controlled electrode structure and water management

In this study, we first attempted to discover the optimal configuration of membrane-electrode assemblies(MEAs) used to achieve a high performance of direct hydrazine fuel cells(DHFCs). We have investigated the effect of water management and the electrode thickness on the performance of DHFCs, depending on the hydrophobicity of the gas diffusion layers in the cathode and the catalyst loading in the anode with the carbon-supported Ni, synthesized by a polyol process. With the optimal water management and electrode thickness, the MEA constructed using the as-prepared Ni/C anode catalyst containing the metallic and low oxidative state and ultra-low Pt loading cathode reduced the ohmic resistance and mass transfer limitation in the current-voltage curves observed for the alkaline DHFC, achieving an impressive power performance over 500 mW cm^(–2).

Biomass-derived bifunctional electrocatalysts for oxygen reduction and evolution reaction: A review

Oxygen electrode catalysts are important as inter-conversion of O_(2) and H_(2)O is crucial for energy technologies.However,the sluggish kinetics of oxygen reduction and evolution reactions(ORR and OER)are a hindrance to their scalable production,whereas scarce and costly Pt and Ir/Ru-based catalysts with the highest electrocatalytic activity are commercially unviable.Since good ORR catalysts are not always efficient for OER and vice versa,so bifunctional catalysts on which OER and ORR occurs on the same electrode are very desirable.Alternative catalysts based on heteroatom-doped carbon nanomaterials,though showed good electrocatalytic activity yet their high cost and complex synthesis is not viable for scalable production.To overcome these drawbacks,biomass-derived heteroatom-doped porous carbons have recently emerged as low-cost,earth-abundant,renewable and sustainable environment-friendly materials for bifunctional oxygen catalysts.The tunable morphology,mesoporous structure and high concentration of catalytic active sites of these materials due to heteroatom(N)-doping could further enhance their ORR and OER activity,along with tolerance to methanol crossover and good durability.Thus,biomassderived heteroatom-doped porous carbons with large surface area,rich edge defects,numerous micropores and thin 2 D nanoarchitecture could be suitable as efficient bifunctional oxygen catalysts.In the present article,synthesis,N-doping,ORR/OER mechanism and electrocatalytic performance of biomassderived bifunctional catalysts has been discussed.The selected biomass(chitin,eggs,euonymus japonicas,tobacco,lysine and plant residue)except wood,act as both C and N precursor,resulting in N selfdoping of porous carbons that avoids the use of toxic chemicals,thus making the synthesis a facile and environment-friendly green process.The synthetic strategy could be further optimized to develop future biomass-based N self-doped porous carbons as metal-free high performance bifunctional oxygen catalysts for commercial energy applications.Recent advances and the importance of biomass-based bifunctional oxygen catalysts in metal-air batteries and fuel cells has been highlighted.The material design,perspectives and future directions in this field are also provided.