CoSe2 nanoparticles anchored on CoNC carbon nanoplates as bifunctional electrocatalyst for flexible rechargeable Zn-air batteries.

A flexible solid rechargeable Zn-air battery for advanced energy conversion and storage has extensive applications in portable electric sources, wildlife rescue and flexible wearable systems. Herein, the CoSe2 nanoparticles anchored on cobalt-embedded N-doping carbon nanoplates (CoSe2/CoNC) is developed as a highly active bifunctional catalyst via pyrolysis and selenization of bimetallic zeolitic imidazolate frameworks containing Zn and Co. The introduction of inactive Zn generates strong electrochemically active surface areas due to the synergistic effect between CoSe2 nanoparticles and CoNC matrix. Further, CoSe2/CoNC exhibits prominent Zn-air battery performance and even outperforms the commercially available noble-metal catalysts. Notably, a high-rate flexible Zn-air battery enabled by an alkaline composite polyacrylic acid-carboxymethyl cellulose electrolyte delivers the open-circuit potential of 1.51 V. The battery offers high wearability and performs very well under various conditions, such as soaking, drilling and sewing.

Epitaxially Grown Heterostructured SrMn3 O6-x -SrMnO3 with High-Valence Mn3+/4+ for Improved Oxygen Reduction Catalysis.

Heterostructured catalysts show outstanding performance in electrochemical reactions owing to their beneficial interfacial properties. However, the rational design of heterostructured catalysts with the desired interfacial properties and charge-transfer characteristics is challenging. Herein, we developed a SrMn3 O6-x -SrMnO3 (SMOx -SMO) heterostructure through epitaxial growth, which demonstrated excellent electrocatalyst performance for the oxygen reduction reaction (ORR). The formation of high-valence Mn3+/4+ is beneficial for promoting a positive shift in the position of the d-band center, thereby optimizing the adsorption and desorption of ORR intermediates on the heterojunction surface and resulting in improved catalytic activity. When SMOx -SMO was applied as an air-electrode catalyst in a rechargeable zinc-air battery, a high output voltage and power density was achieved, with performance comparable to a battery prepared with Pt/C-IrO2 air-electrode catalysts, albeit with much better cycling stability.

Filling the Charge-Discharge Voltage Gap in Flexible Hybrid Zinc-Based Batteries by Utilizing a Pseudocapacitive Material.

The high charge-discharge voltage gap is one of the main bottlenecks of zinc-air batteries (ZABs) because of the kinetically sluggish oxygen reduction/evolution reactions (ORR/OER) on the oxygen electrode side. Thus, an efficient bifunctional catalyst for ORR and OER is highly desired. Herein, honeycomb-like MnCo2 O4.5 spheres were used as an efficient bifunctional electrocatalyst. It was demonstrated that both ORR and OER catalytic activity are promoted by MnIV -induced oxygen vacancy defects and multiple active sites. Importantly, the multivalent ions present in the material and its defect structure endow stable pseudocapacitance within the inactive region of ORR and OER; as a result, a low charge-discharge voltage gap (0.43 V at 10 mA cm-2 ) was achieved when it was employed in a flexible hybrid Zn-based battery. This mechanism provides unprecedented and valuable insights for the development of next-generation metal-air batteries.

Surface Reorganization on Electrochemically-Induced Zn-Ni-Co Spinel Oxides for Enhanced Oxygen Electrocatalysis.

Herein, we highlight redox-inert Zn2+ in spinel-type oxide (ZnX Ni1-X Co2 O4 ) to synergistically optimize physical pore structure and increase the formation of active species on the catalyst surface. The presence of Zn2+ segregation has been identified experimentally and theoretically under oxygen-evolving condition, the newly formed VZn -O-Co allows more suitable binding interaction between the active center Co and the oxygenated species, resulting in superior ORR performance. Moreover, a liquid flow Zn-air battery is constituted employing the structurally optimized Zn0.4 Ni0.6 Co2 O4 nanoparticles supported on N-doped carbon nanotube (ZNCO/NCNTs) as an efficient air cathode, which presents remarkable power density (109.1 mW cm-2 ), high open circuit potential (1.48 V vs. Zn), excellent durability, and high-rate performance. This finding could elucidate the experimentally observed enhancement in the ORR activity of ZnX Ni1-X Co2 O4 oxides after the OER test.

Redox-Inert Fe3+ Ions in Octahedral Sites of Co-Fe Spinel Oxides with Enhanced Oxygen Catalytic Activity for Rechargeable Zinc-Air Batteries.

Bimetallic cobalt-based spinel is sparking much interest, most notably for its excellent bifunctional performance. However, the effect of Fe3+ doping in Co3 O4 spinel remains poorly understood, mainly because the surface state of a catalyst is difficult to characterize. Herein, a bifunctional oxygen electrode composed of spinel Co2 FeO4 /(Co0.72 Fe0.28 )Td (Co1.28 Fe0.72 )Oct O4 nanoparticles grown on N-doped carbon nanotubes (NCNTs) is designed, which exhibits superior performance to state-of-the-art noble metal catalysts. Theoretical calculations and magnetic measurements reveal that the introduction of Fe3+ ions into the Co3 O4 network causes delocalization of the Co 3d electrons and spin-state transition. Fe3+ ions can effectively activate adjacent Co3+ ions under the action of both spin and charge effect, resulting in the enhanced intrinsic oxygen catalytic activity of the hybrid spinel Co2 FeO4 . This work provides not only a promising bifunctional electrode for zinc-air batteries, but also offers a new insight to understand the Co-Fe spinel oxides for oxygen electrocatalysis.