Engineering High-Spin State Cobalt Cations in Sulfide Spinel for Enhancing Water Oxidation

Cr-Substituted SrCoO3-δ Perovskite with Abundant Oxygen Vacancies for High-Energy and Durable Low-Temperature Antifreezing Flexible Supercapacitor

Developing high-performance electrodes for flexible antifreezing energy storage devices has been a significant challenge with the increasing demand for portable components. In this work, Cr-substituted SrCoO3-δ perovskites were first proposed as potential low-temperature supercapacitor electrode materials. The high-valence Cr6+ ([Ne]3s23p6) substitution favors a high-spin state of Co ions with enhanced electronic repulsion effect, ultimately forming a stable cubic structure with high conductivity. Accordingly, the modification strategies of SrCoO3 through the p6 configuration cation substitution have been improved. As a result, the asymmetric SrCo0.95Cr0.05O3-δ@CC//PPy@CC device exhibited a high energy density of 44.90 Wh kg-1 at 902.01 W kg-1 and maintained a 95.8% specific capacitance after 10,000 cycles, demonstrating an ultralong cyclic stability. The dramatically improved electrochemical performance was attributed to the stabilized crystal structure, increased oxygen vacancy, and accelerated oxygen diffusion rate. Furthermore, a quasi-solid-state supercapacitor with ethylene glycol (EG)-modified KOH/PVA organohydrogel electrolyte was developed through an advance in situ-integrated strategy. After bending at 180° for 1000 cycles, only a 9.7% capacity decay was observed. Even under -40 °C, the supercapacitor has a large energy density of 46.94 μWh cm-2. The present work represents the initial investigation into utilizing perovskite materials for antifreezing energy storage device, thereby confirming their potential application as low-temperature electronic components.

Boosting the ORR/OER Activity of Cobalt-Based Nano-Catalysts by Co 3d Orbital Regulation

The transition metal oxides/sulfides are considered promising catalysts due to their abundant resources, facile synthesis, and reasonable electrocatalytic activity. Herein, a significantly improved intrinsic catalytic activity is achieved for constructing a Co-based nanocrystal (Co-S@NC) with the coordination of Co─S, Co─S─C, and Co─Nx─C. The calculational and experimental results demonstrate that the diversified chemical environment of Co-cations induces the transition of 3d orbitals to a high spin-state that exhibits the coexistence of Co2+ with fully occupied dπ orbitals and Co3+ with unpaired electrons in dπ orbitals. The diverse dπ orbitals occupation contributes to an elevated d-band center of Co ions, which accelerates oxygen reduction reaction and oxygen evolution reaction electrocatalytic kinetics of the Co-S@NC nanocrystal. Therefore, the Li-O2 batteries with Co-S@NC as cathode catalyst exhibit 300 cycles at the current density of 500 mA g-1 with a cut-off capacity of 1000 mAh g-1. Moreover, the ultrahigh discharge specific capacity of 34 587 mAh g-1 is obtained at a current density of 1000 mA g-1, corresponding to the energy density 949 Wh kg-1 of a prototype Li-O2 battery. The study on 3d orbital regulation of nanocrystals provides an innovative strategy for bifunctional electrocatalysts toward the practical application of metal-air batteries.

Direct Capturing and Regulating Key Intermediates for High-Efficiency Oxygen Evolution Reactions

Developing efficient oxygen evolution reaction (OER) electrocatalysts can greatly advance the commercialization of proton exchange membrane (PEM) water electrolysis. However, the unclear and disputed reaction mechanism and structure-activity relationship of OER pose significant obstacles. Herein, the active site and intermediate for OER on AuIr nanoalloys are simultaneously identified and correlated with the activity, through the integration of in situ shell-isolated nanoparticle-enhanced Raman spectroscopy and X-ray absorption spectroscopy. The AuIr nanoalloys display excellent OER performance with an overpotential of only 246 mV to achieve 10 mA cm-2 and long-term stability under strong acidic conditions. Direct spectroscopic evidence demonstrates that * OO adsorbed on IrOx sites is the key intermediate for OER, and it is generated through the O-O coupling of adsorbed oxygen species directly from water, providing clear support for the adsorbate evolution mechanism. Moreover, the Raman information of the * OO intermediate can serve as a universal "in situ descriptor" that can be obtained both experimentally and theoretically to accelerate the catalyst design. It unveils that weakening the interactions of * OO on the catalysts and facilitating its desorption would boost the OER performance. This work deepens the mechanistic understandings on OER and provides insightful guidance for the design of more efficient OER catalysts.