Regulating non-precious transition metal nitrides bifunctional electrocatalysts through surface/interface nanoengineering for air-cathodes of Zn-air batteries

Zn-air batteries(ZABs),especially the secondary batteries,have engrossed a great interest because of its high specific energy,economical and high safety.However,due to the insufficient activity and stability of bifunctional electrocatalysts for air-cathode oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)processes,the practical application of rechargeable ZABs is seriously hindered.In the effort of developing high active,stable and cost-effective electrocatalysts,transition metal nitrides(TMNs)have been regarded as the candidates due to their high conductivity,strong corrosion-resistance,and bifunctional catalytic performance.In this paper,the research progress in TMNs-based material as ORR and OER electrocatalysts for ZABs is discussed with respect to their synthesis,chemical/physical characterization,and performance validation/optimization.The surface/interface nanoengineering strategies such as defect engineering,support binding,heteroatom introduction,crystal plane orientation,interface construction and small size effect,the physical and chemical properties of TMNs-based electrocatalysts are emphasized with respect to their structures/morphologies,composition,electrical conductivity,specific surface area,chemical stability and corrosion resistance.The challenges of TMNs-based materials as bifunctional air-cathode electrocatalysts in practical application are evaluated,and numerous research guidelines to solve these problems are put forward for facilitating further research and development.

Structure adapting of bulk FeS_(2) micron particles and the corresponding anode for high performance sodium-ion batteries

The practical application of Pyrite iron disulfide (FeS_(2)) as anode material of sodium-ion battery is limitedby its low electronic conductivity, large volume changes during charge/discharge. To overcome thesechallenges, a novel structure design single-walled carbon nanotubes (SWCNTs) composited polyaniline(PANI)-wrapped FeS_(2) (FeS_(2)-PANI-SWCNTs) electrodes are successfully achieved in this work. PANI canprotect the FeS_(2) particles from collapse and offer a protective layer to relive the polysulfides shuttlingeffect, and also promote the electron and Naþ diffusion during the chemical conversion process. Underthe dual protection of PANI and SWCNTs, the FeS_(2)-PANI-SWCNTs film electrode demonstrates a goodstructural integrity, which accounts for the excellent rate capability and long cycling performance. Inaddition, the PANI coating and SWCNT network in the fabricated electrode can synergistically anchorpolysulfides and therefore strongly suppress shuttle effect during the chargeedischarge processes,resulting in less capacity loss. The anode with a loading 3.2 mg cm 2 of FeS_(2) coated with PANI exhibitsthe initial coulombic efficiency of 81.5% and delivers a specific capacity of 625.8 mAh g^(-1) after 100 cyclesat 200 mA g^(-1). High flexible and binder-free FeS_(2)-PANI-SWCNTs film anode demonstrates a reversiblecapacity of 537 mAh g^(-1) after 550 cycles at 1 A g^(-1). This research may offer an efficient method toimprove electrochemical performance of the metal sulfides in sodium-ion batteries.