Green bridge between waste and energy: conversion the rotten wood into cathode for functional Zn-air battery

Biochar made from Luffa cylindrica and applied as a bifunctional electrocatalyst in Zn-air batteries

Biochar has been prepared by pyrolysis of Luffa cylindrica (the vegetable sponge produced by Luffa aegiptiaca) and activated by mixing the pyrolyzed powder with KOH and pyrolyzed again. Non-activated and activated biochar have both been structurally and then electrochemically characterized to record their differences and assess their suitability as bifunctional oxygen reduction and oxygen evolution reaction electrocatalysts in Zn-air batteries. Non activated biochar carries several functional groups; however, the activation procedure led to a material with mainly O and Mg groups. Biochar activation improved its electrocatalytic properties, but both activated and non-activated luffa biochar were functional as bifunctional electrocatalysts to a satisfactory degree. This is justified by the fact that both carried a large percentage of carbon and graphitic carbon. The advantage of the non-activated biochar versus the activated biochar was its variety of functional groups while that of the activated biochar was its large specific surface area.

Biomass-Derived Catalytically Active Carbon Materials for the Air Electrode of Zn-Air Batteries

Given the growing environmental and energy problems, developing clean, renewable electrochemical energy storage devices is of great interest. Zn-air batteries (ZABs) have broad prospects in energy storage because of their high specific capacity and environmental friendliness. The unavailability of cheap air electrode materials and effective and stable oxygen electrocatalysts to catalyze air electrodes are main barriers to large-scale implementation of ZABs. Due to the abundant biomass resources, self-doped heteroatoms, and unique pore structure, biomass-derived catalytically active carbon materials (CACs) have great potential to prepare carbon-based catalysts and porous electrodes with excellent performance for ZABs. This paper reviews the research progress of biomass-derived CACs applied to ZABs air electrodes. Specifically, the principle of ZABs and the source and preparation method of biomass-derived CACs are introduced. To prepare efficient biomass-based oxygen electrocatalysts, heteroatom doping and metal modification were introduced to improve the efficiency and stability of carbon materials. Finally, the effects of electron transfer number and H2O2 yield in ORR on the performance of ZABs were evaluated. This review aims to deepen the understanding of the advantages and challenges of biomass-derived CACs in the air electrodes of ZABs, promote more comprehensive research on biomass resources, and accelerate the commercial application of ZABs.

Biochar from olive tree twigs and spent malt rootlets as electrodes in Zn-air batteries

Biochars, i.e. porous carbons obtained by pyrolysis of biomass, can act as electrocatalysts for oxygen evolution and oxygen reduction reaction. In the present work, two biochars have been prepared by using materials of completely different biomass origin: olive-tree twigs and spent malt rootlets (brewery wastes). Both biomass species were subjected to pyrolysis under limited oxygen supply and then they were activated by mixing with KOH and pyrolysis again. The obtained biochars were characterized by several techniques in order to determine their structural characteristics and the composition of their active components. Despite their different origin, the two biochars demonstrated similar structural and compositional characteristics thus highlighting the importance of the pyrolysis and activation procedure. Both biochars were used as electrocatalysts in the operation of rechargeable Zn-air batteries, where they also demonstrated similar electrocatalytic capacities with only a small advantage gained by olive-tree-twigs biochar. Compared to bare nanoparticulate carbon (carbon black), both biochars demonstrated a marked advantage towards oxygen evolution reaction.