Interfacial Electronic Structure Modulation of Hierarchical Co(OH)F/CuCo2S4 Nanocatalyst for Enhanced Electrocatalysis and Zn-Air Batteries Performances

Defect Engineering for Enhanced Electrocatalytic Oxygen Reaction on Transition Metal Oxides: The Role of Metal Defects

Metal defect engineering is a highly effective strategy for addressing the prevalent high overpotential issues associated with transition metal oxides functioning as dual-function commercial oxygen reduction reaction/oxygen evolution reaction catalysts for increasing their activity and stability. However, the high formation energy of metal defects poses a challenge to the development of strategies to precisely control the selectivity during metal defect formation. Here, density functional theory calculations are used to demonstrate that altering the pathway of metal defect formation releases metal atoms as metal chlorides, which effectively reduces the formation energy of defects. The metal defects on the monometallic metal oxide surface (Mn, Fe, Co, and Ni) are selectively produced using chlorine plasma. The characterization and density functional theory calculations reveal that catalytic activity is enhanced owing to electronic delocalization induced by metal defects, which reduces the theoretical overpotential. Notably, ab initio molecular dynamics calculations, ex situ XPS, and in situ ATR-SEIRAS suggest that metal defects effectively improve the adsorption of reactive species on active sites and enhance the efficiency of product desorption, thereby boosting catalytic performance.

Phase Engineering and Synchrotron-Based Study on Two-Dimensional Energy Nanomaterials

In recent years, there has been significant interest in the development of two-dimensional (2D) nanomaterials with unique physicochemical properties for various energy applications. These properties are often derived from the phase structures established through a range of physical and chemical design strategies. A concrete analysis of the phase structures and real reaction mechanisms of 2D energy nanomaterials requires advanced characterization methods that offer valuable information as much as possible. Here, we present a comprehensive review on the phase engineering of typical 2D nanomaterials with the focus of synchrotron radiation characterizations. In particular, the intrinsic defects, atomic doping, intercalation, and heterogeneous interfaces on 2D nanomaterials are introduced, together with their applications in energy-related fields. Among them, synchrotron-based multiple spectroscopic techniques are emphasized to reveal their intrinsic phases and structures. More importantly, various in situ methods are employed to provide deep insights into their structural evolutions under working conditions or reaction processes of 2D energy nanomaterials. Finally, conclusions and research perspectives on the future outlook for the further development of 2D energy nanomaterials and synchrotron radiation light sources and integrated techniques are discussed.

Heterostructured Ultrathin Two-Dimensional Co-FeOOH Nanosheets@1D Ir-Co(OH)F Nanorods for Efficient Electrocatalytic Water Splitting

It is highly desirable to develop high-performance and robust electrocatalysts for overall water splitting, as the existing electrocatalysts exhibit poor catalytic performance toward hydrogen and oxygen evolution reactions (HER and OER) in the same electrolytes, resulting in high cost, low energy conversion efficiency, and complicated operating procedures. Herein, a heterostructured electrocatalyst is realized by growing Co-ZIF-67-derived 2D Co-doped FeOOH on 1D Ir-doped Co(OH)F nanorods, denoted as Co-FeOOH@Ir-Co(OH)F. The Ir-doping couples with the synergy between Co-FeOOH and Ir-Co(OH)F effectively modulate the electronic structures and induce defect-enriched interfaces. This bestows Co-FeOOH@Ir-Co(OH)F with abundant exposed active sites, accelerated reaction kinetics, improved charge transfer abilities, and optimized adsorption energies of reaction intermediates, which ultimately boost the bifunctional catalytic activity. Consequently, Co-FeOOH@Ir-Co(OH)F exhibits low overpotentials of 192/231/251 and 38/83/111 mV at current densities of 10/100/250 mA cm^-2 toward the OER and HER in a 1.0 M KOH electrolyte, respectively. When Co-FeOOH@Ir-Co(OH)F is used for overall water splitting, cell voltages of 1.48/1.60/1.67 V are required at current densities of 10/100/250 mA cm^-2. Furthermore, it possesses outstanding long-term stability for OER, HER, and overall water splitting. Our study provides a promising way to prepare advanced heterostructured bifunctional electrocatalysts for overall alkaline water splitting.

Synergetic Metal Defect and Surface Chemical Reconstruction into NiCo2 S4 /ZnS Heterojunction to Achieve Outstanding Oxygen Evolution Performance

Defect and interface engineering are recognized as effective strategies to regulate electronic structure and improve activity of metal sulfide. However, the practical application of sulfide is restricted by their low conductivity and rapid decline in activity derived from large volume fluctuation during electrocatalysis process. More importantly, the determination of exact active site of sulfide is complicated due to the inevitable electrochemical reconstruction. Herein, ZnS nanoparticles with Zn defect are anchored onto the surface of NiCo₂ S₄ nanosheet to construct NiCo₂ S₄ /ZnS hybrids, which exhibit outstanding oxygen evolution performance with an ultralow overpotential of 140 mV. The anchoring of defective ZnS nanoparticles inhibit the volume expansion of NiCo₂ S₄ nanosheet during the cycling process. Density-functional theory reveals that the build-in interfacial potential and Zn defect can facilitate the thermodynamic formation of *O to *OOH, thus improve their intrinsic activity.

Hydrophobic POM Electrocatalyst Achieves Low Voltage "Charge" in Zn-Air Battery Coupled with Bisphenol A Degradation

Zn-air batteriesare a perspective power source for grid-storage. But, after they are discharged at1.1 to 1.2 V, large overpotential is required for their charging (usually 2.5 V). This is due to a sluggish oxygen evolution reaction (OER). Incorporating organic pollutants into the cathode electrolyte is a feasible strategy for lowering the required charging potential. In the discharge process, the related oxygen reduction reaction, hydrophobic electrocatalysts are more popular than hydrophilic ones. Here, a hydrophobic bifunctional polyoxometalate electrocatalyst is synthesized by precise structural design. It shows excellent activities in both bisphenol A degradation and oxygen reduction reactions. In bisphenol A containing electrolyte, to achieve 100 mA ⋅ cm^-2 , its potential is only 1.32 V, which is 0.34 V lower than oxygen evolution reaction. In the oxygen reduction reaction, this electrocatalyst follows the four-electron mechanism. In both bisphenol A degradation and oxygen reduction reactions, it shows excellent stability. With this electrocatalyst as cathode material and bisphenol A containing KOH as electrolyte, a Zn-air battery was assembled. When "charged" at 85 mA ⋅ cm^-2 , it only requires 1.98 V. Peak power density of this Zn-air battery reaches 120.5 mW ⋅ cm^-2 . More importantly, in the "charge" process, bisphenol A is degraded, which achieves energy saving and pollutant removal simultaneously in one Zn-air battery.

CuCo2 S4 -rGO Microflowers: First-Principle Calculation and Application in Energy Storage

This paper demonstrates the ability of a CuCo₂ S₄ -reduced graphene oxide (rGO) composite to perform robust electrochemical performances applying to supercapacitors (SCs) and lithium ion batteries (LIBs). The first-principle calculation based on density functional theory is conducted to study the electronic property of CuCo₂ O₄ and CuCo₂ S₄ and provide a theoretical basis for this work. Then, the 3D spinel-structured CuCo₂ O₄ and CuCo₂ S₄ microflowers are synthesized and compared as electrodes for both SCs and LIBs. The CuCo₂ S₄ microflowers can provide a larger specific surface area, which enlarges the contact area between the electrode material and the electrolyte and contributes to high-efficiency electrochemical reactions. The reduced graphene oxides are coated on the CuCo₂ S₄ microflowers, therefore effectively increasing the conductivity, and further absorbing the stress produced in the reaction process. As an electrode of a symmetric supercapacitor, the optimized CuCo₂ S₄ -rGO composite exhibits an energy density of 16.07 Wh kg^-1 and a maximum power density of 3600 W kg^-1 . Moreover, the CuCo₂ S₄ -rGO composite can also be used as an anode for lithium ion batteries, exhibiting a reversible capacity of 1050 mAh g^-1 after 140 cycles at the current density of 200 mA g^-1 . The galvanostatic intermittence titration techniques also reveal superior Li-ion diffusion behavior of the CuCo₂ S₄ -rGO composite during redox reactions.

Dual-modulation of electronic structure and active sites of PtCu nanodendrites by surface nitridation to achieve efficient methanol electrooxidation and oxygen reduction reaction

A facile method to prepare PtCu nanodendrites rich in multiple active sites was reported using pyridine as a surface modifier. They exhibit outstanding electrocatalytic performance towards ORR and MOR in acidic medium.

MOF-derived hierarchical 3D bi-doped CoP nanoflower eletrocatalyst for hydrogen evolution reaction in both acidic and alkaline media

A 3D hierarchical Bi-doped CoP nanoflowers electrocatalyst is developed based on a MOF self-sacrifice strategy. The 3% Bi/CoP catalyst delivers a current density of 10 mA cm⁻² at low overpotentials of 122 mV in alkaline electrolyte and 150 mV in acidic electrolyte.