Unraveling the Synergistic Effect of Heteroatomic Substitution and Vacancy Engineering in CoFe2O4 for Superior Electrocatalysis Performance.

Metal ion substitution and anion exchange are two effective strategies for regulating the electronic and geometric structure of spinel. However, the optimal location of foreign metallic cations and the exact role of these metals and anions remain elusive. Herein, CoFe2O4-based hollow nanospheres with outstanding oxygen evolution reaction activity are prepared by Cr3+ substitution and S2- exchange. X-ray absorption spectra and theoretical calculations reveal that Cr3+ can be precisely doped into octahedral (Oh) Fe sites and simultaneously induce Co vacancy, which can activate adjacent tetrahedral (Td) Fe3+. Furthermore, S2- exchange results in structure distortion of Td-Fe due to compressive strain effect. The change in the local geometry of Td-Fe causes the *OOH intermediate to deviate from the y-axis plane, thus enhancing the adsorption of the *OOH. The Co vacancy and S2- exchange can adjust the geometric and electronic structure of Td-Fe, thus activating the inert Td-Fe and improving the electrochemical performance.

S-Block Potassium Single-atom Electrocatalyst with K-N4 Configuration Derived from K+ /Polydopamine for Efficient Oxygen Reduction.

Currently, single-atom catalysts (SACs) research mainly focuses on transition metal atoms as active centers. Due to their delocalized s/p-bands, the s-block main group metal elements are typically regarded as catalytically inert. Herein, an s-block potassium SAC (K-N-C) with K-N4 configuration is reported for the first time, which exhibits excellent oxygen reduction reaction (ORR) activity and stability under alkaline conditions. Specifically, the half-wave potential (E1/2 ) is up to 0.908 V, and negligible changes in E1/2 are observed after 10,000 cycles. In addition, the K-N-C offers an exceptional power density of 158.1 mW cm-2 and remarkable durability up to 420 h in a Zn-air battery. Density functional theory (DFT) simulations show that K-N-C has bifunctional active K and C sites, can optimize the free energy of ORR reaction intermediates, and adjust the rate-determining steps. The crystal orbital Hamilton population (COHP) results showed that the s orbitals of K played a major role in the adsorption of intermediates, which was different from the d orbitals in transition metals. This work significantly guides the rational design and catalytic mechanism research of s-block SACs with high ORR activity.

Constructing Precise Coordination of Nickel Active Sites on Hierarchical Porous Carbon Framework for Superior Oxygen Reduction.

Single-atom catalysts (SACs) with specific coordination environment are expected to be efficient electrocatalysts for oxygen reduction reaction (ORR). Herein, NiN4 C10 coordination site is constructed through encapsulating Ni2+ into the cavity of ZIF-8 as a self-sacrificing precursor and anchoring it on 3D N-doped carbon frameworks. The NiN4 C10 catalyst shows excellent ORR activity and stability, with a high half-wave potential (0.938 V vs RHE), which is currently the best performances in Ni-based SACs. The remarkable performance with high ORR activity in alkaline solution is attributed to the single-atom nickel active sites with faster electron transport and suitable electronic structure. Moreover, the power density of zinc-air battery assembled by NiN4 C10 as cathode is 47.1% higher than that of the commercial Pt/C. This work not only provides a facile method to prepare extremely active Ni-based SACs, but also studies the intrinsic mechanism toward the oxygen reduction reaction under alkaline condition.

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.

Achieving Superior Electrocatalytic Performance by Surface Copper Vacancy Defects during Electrochemical Etching Process.

Vacancy defects of catalysts have been extensively studied and proven to be beneficial to various electrocatalytic reactions. Herein, an ultra-stable three-dimensional PtCu nanowire network (NNW) with ultrafine size, self-supporting rigid structure, and Cu vacancy defects has been developed. The vacancy defect-rich PtCu NNW exhibits an outstanding performance for the oxygen reduction reaction (ORR), with a mass activity 14.1 times higher than for the commercial Pt/C catalyst (20 %.wt, JM), which is currently the best performance. The mass activity of the PtCu NNW for methanol oxidation reaction (MOR) is 17.8 times higher than for the commercial Pt/C catalyst. Density-functional theory (DFT) calculations indicate that the introduction of Cu vacancies enhances the adsorption capacity of Pt atoms to the HO* intermediate and simultaneously weakens the adsorption for the O* intermediate. This work presents a facile strategy to assemble efficient electrocatalysts with abundant vacancy defects, at the same time, provides an insight into the ORR mechanism in acidic solution.

Incorporating a built-in electric field into a NiFe LDH heterojunction for enhanced oxygen evolution and urea oxidation.

Herein, a N-doped carbon-supported Co and NiFe LDH (Co-NC@NiFe LDH) array was developed, which demonstrated superior catalytic activities for both the OER and UOR in an alkaline medium. The intrinsic electron transfer is effectively regulated by the construction of a built-in electric field, which reduces the reaction energy barrier and consequently leads to a significant enhancement in electrocatalytic activity.

The 3d-4f electron transition of the CoS2/CeO2 heterojunction for efficient oxygen evolution.

CoS2/CeO2, exhibiting the 3d-4f orbital coupling effect, is developed and shows exceptional OER activity, with an overpotential of 140 mV at 10 mA cm-2. DFT calculation and Raman spectra show the existence of a d-p-f electron transport ladder that can accelerate electron transfer through the Co-O(S)-Ce bond, optimize the adsorption free energy, and enhance the catalytic activity.

Synergetic of Built-In Electric Field and Sulfur Defects in Co@Co9S8 Mott-Schottky To Achieve High-Efficiency Zinc-Air Battery Performance.

The slow kinetics of the bifunctional (OER/ORR) oxygen electrocatalyst is the bottleneck problem restricting the performance of zinc-air batteries (ZABs). The design and synthesis of an efficient and stable electrocatalyst at the air cathode to improve the performance of ZABs is of great significance for the development of sustainable energy conversion devices. Herein, we have developed a sulfur vacancy-rich Mott-Schottky catalyst (Co@Co9S8-NCNT), which shows superior ORR/OER bifunctional electrochemical activity and stability. Specifically, the OER overpotential is only 210 mV at 10 mA cm-2, and the half-wave potential (E1/2) of ORR is up to 0.88 V. Furthermore, a ZAB has been assembled using the Co@Co9S8-NCNT, which delivers a high power density (196.7 mW cm-2) and an open-circuit voltage (1.501 V), showing excellent battery performance. Density functional theory calculations demonstrate that the Co@Co9S8 Mott-Schottky heterojunction and S vacancy defects are beneficial to elevate the d-band central energy level to the Fermi level, significantly enhancing the adsorption/desorption capacity of oxygen-containing intermediates, thereby effectively improving the OER activity. Moreover, the N-doped carbon nanotubes can promote the continuous electron transfer between the metal and semiconductor interface. This work proposes a valid method for the construction and structural regulation of Mott-Schottky catalysts and offers new insights into the development of catalytic materials for energy conversion equipment.

Amorphous/crystalline heterostructure of NiFe (oxy)hydroxides for efficient oxygen evolution and urea oxidation.

A V-doped amorphous/crystalline heterostructure of NiFe (oxy)hydroxide with nanoflower morphology is developed, which exhibits excellent OER and UOR catalytic activities. V doping changes the local charge density, lowers the reaction barrier, and optimizes the electron arrangement of the NiFe LDH catalyst.

Bimetallic doping engineering of Ni3S2 nanosheets originating from NiFe layered double hydroxide for efficient overall water splitting.

Fe, Mo-doped Ni3S2 nanosheets that are derived from NiFe-LDH by structural transformation have been successfully developed. The obtained Fe, Mo-Ni3S2 exhibits a low overpotential of 67 mV to enable a current density of 10 mA cm-2 for the HER and the overpotential for the OER is only 240 mV. Besides, the current density of 10 mA cm-2 can be achieved with a voltage of 1.53 V in a two-electrode hydrolysis device.

Tuning the Electronic Structure of CoP Embedded in N-Doped Porous Carbon Nanocubes Via Ru Doping for Efficient Hydrogen Evolution.

Designing and synthesizing stable electrocatalysts with outstanding performance for water splitting is an arduous and urgent task. Herein, Ru-anchored CoP embedded in N-doped porous carbon nanocubes (Ru-CoP/NCs) is successfully prepared. The Ru-CoP/NC reveals superior hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) properties and stability under alkaline conditions, and the corresponding overpotentials are 22 and 330 mV at 10 mA·cm-2, respectively. The unique N-doped porous carbon nanocube could boost the conductivity, and the electronic structure of CoP can be adjusted by the anchoring of Ru. Therefore, the strong interaction between Ru atoms and CoP improves the hydrogen adsorption on the catalyst, hence boosting the HER/OER performance of the Ru-CoP/NC catalyst. This work provides a facile method to exploit high-performance catalysts for water splitting.

Solvent assistance induced surface N-modification of PtCu aerogels and their enhanced electrocatalytic properties.

A facile method involving the nitrogen modification of PtCu aerogel surfaces with N-methyl pyrrolidone as the sole nitrogen source is reported. The half wave potential (E1/2) of the PtCu aerogels was 0.932 V and the electrochemical active surface area (ECSA) was 102.04 m2 g-1 for the oxygen reduction reaction (ORR), and the mass activity (MA) for the methanol electrooxidation reaction (MOR) was measured to be 4.08 A mg-1, values better than those of a commercial Pt/C catalyst and other reported Pt-based catalysts.

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 oxygen reduction reaction and methanol electrooxidation 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 nanoflower electrocatalyst has been developed based on a MOF self-sacrifice strategy. 3% Bi/CoP delivers a current density of 10 mA cm-2 at low overpotentials of 122 mV in alkaline electrolyte and 150 mV in acidic electrolyte, respectively. DFT calculations demonstrate that Bi doping can synergistically optimize the binding free energy of H* on the CoP (202) facet and ultimately improve the HER performance.

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

The exploration of robust multifunctional electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is a continuing challenge for the sustainable energy sources. However, as the key reactions in renewable metal-air batteries and fuel cells, the energy conversion efficiencies of ORR and OER are greatly affected by their reaction kinetics. In addition to designing excellent electrocatalysts, new methods to stabilize the electrolyte/electrode interfaces are urgently needed. Herein, a hierarchical Co(OH)F/CuCo2S4 hybrid was created as an efficient catalyst for OER and ORR in alkaline media. Combining spinel ferrite with the hydroxide can greatly boost their catalytic performance. The optimal Co(OH)F/CuCo2S4 hybrid exhibits superior OER performance and durable stability, as demonstrated by an ultralow overpotential of 230 mV at 10 mA·cm-2. The onset potential and the half-wave potential in 0.1 M KOH solution for ORR are 0.88 and 0.80 V, respectively. Furthermore, the Co(OH)F/CuCo2S4 hybrid served as a catalyst in Zn air batteries catalyst exhibits a low overpotential of 1.12 V at 50.0 mA·cm-2, large power density of 144 mW·cm-2, and a long electrochemical lifetime of 118 h (118 cycles), which is even better than those of the Pt/C and RuO2 catalysts. The rational integration of spinel and hydroxide at the interface can provide multifunctional electrocatalysis and possess a high reactivity for oxygen conversion. Synergistic coupling effect and interfacial electronic interaction between Co(OH)F and CuCo2S4 can significantly enhance the electron transfer rate, and these synergistic advantages enable the heterogeneous structure of the multifunctional electrocatalyst to produce excellent catalytic performance.