Biomass-derived nonprecious metal catalysts for oxygen reduction reaction: The demand-oriented engineering of active sites and structures

Oxygen reduction reaction(ORR)is an important electrochemical process for renewable energy conversion and storage applications such as fuel cells and metal-air batteries.ORR is sluggish in kinetics and requires a large amount of platinum group metal(PGM)-based catalysts to facilitate its slow reaction rate.Application of precious metals raises the cost and decreases the competitivity of these devices in the market.To address this challenge,PGM-free ORR catalysts have been intensively investigated as an alternative to replace the PGM-based catalysts and to promote the deployment of ORR-related applications.In particular,the biomass holds promising potential to be used as the precursor material for PGM-free ORR catalysts.This pathway has gained more and more attention in recent years.In this review,recent advances regarding biomass-derived ORR catalysts are summarized with a focus on the rational design of both active sites and porous structures which are the two key factors in determining ORR performance of catalysts.At the end,the perspectives of development of biomass-derived catalysts is discussed.

Aqueous Zn-based rechargeable batteries:Recent progress and future perspectives

Benefiting from the advantageous features of high safety,abundant reserves,low cost,and high energy density,aqueous Zn-based rechargeable batteries(AZBs)have received extensive attention as promising candidates for energy storage.To achieve high-performance AZBs with high reversibility and energy density,great efforts have been devoted to overcoming their drawbacks by focusing on the modification of electrode materials and electrolytes.Based on different cathode materials and aqueous electrolytes,the development of aqueous AZBs with different redox mechanisms are discussed in this review,including insertion/extraction chemistries(e.g.,Zn^(2+),alkali metal ion,H^(+),NH_(4)^(+),and so forth dissolution/deposition reactions(e.g.,MnO_(2)/Mn^(2+)),redox couples in flow batteries(e.g.,I_(3)/3I,Br_(2)/Br,and so forth),oxygen electrochemistry(e.g.,O_(2)/OH,O_(2)/O_(2)2),and carbon dioxide electrochemistry(e.g.,CO_(2)/CO,CO_(2)/HCOOH).In particular,the basic reaction mechanisms,issues with the Zn electrode,aqueous electrolytes,and cathode materials as well as their design strategies are systematically reviewed.Finally,the remaining challenges faced by AZBs are summarized,and perspectives for further investigations are proposed.