Porous carbon layers wrapped CoFe alloy for ultrastable Zn-Air batteries exceeding 20,000 charging-discharging cycles

Developing high active and stable bifunctional electrocatalysts towards oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)is essential for the development of rechargeable Zn-air batteries.Herein,a facile strategy to synthesize the porous carbon layers wrapped CoFe alloy(C/CoFe)through the pyrolysis of a homogeneous mixture containing Co,Fe ions and N-doped carbon quantum dots(Ndoped CQDs)was reported.The prepared carbon layers with multi-level pore structures provides more active sites and optimizes the homogeneity of the electron and mass transport.In addition,the carbon layers,which is doped by Co/Fe/N atoms,is responsible for high ORR activity,while the CoFe alloy plays a vital role in OER performance.The as-synthesized catalyst exhibits an excellent bifunctionality for electrochemical oxygen reactions,which is comparable to the commercial Pt/C and IrO2 benchmarks.Owing to the carbon layers protects CoFe alloy nanoparticles from the harsh environment,the rechargeable Znair battery with the C/CoFe catalyst delivers excellent stability during 20,000 charging-discharging cycles.

Boosting the oxygen evolution reaction through migrating active sites from the bulk to surface of perovskite oxides

The oxygen evolution reaction (OER) dominates the efficiency of electrocatalytic water splitting owing to its sluggish kinetics.Perovskite oxides (ABO_(3)) have emerged as promising candidates to accelerate the OER process owing to their high intrinsic activities and tailorable properties.Fe ions in perovskite oxides have been proved to be a highly catalytic element for OER,while some Fe-based perovskites such as SrTi_(0.8)Fe_(0.2)O_(3-δ)(STF) and La_(0.66)Ti_(0.8)Fe_(0.2)O_(3-δ)(LTF) exhibit inferior OER activity.Yet the essential reason is still unclear and the effective method to promote the activity of such perovskite is also lacking.Herein,an in-situ exsolution strategy was proposed to boost the OER by migrating Fe from the bulk to the surface.Significantly enhanced OER activity was achieved on STF and LTF perovskites with surfacedecorated oxygen vacancies and Fe nanoparticles.In addition,theoretical calculation confirmed that the oxygen vacancies and Fe nanoparticle on surface could lower the overpotential of OER by facilitating the adsorption of OH^(-).From this study,migration of the active elements in perovskite is found to be an effective strategy to increase the quantity and activity of active sites,providing new insights and understanding for designing efficient OER catalysts.