Search

Zn−MnO2 batteries have attracted extensive attention for grid‐scale energy storage applications, however, the energy storage chemistry of MnO2 in mild acidic aqueous electrolytes remains elusive and controversial. Using α‐MnO2 as a case study, we developed a methodology by coupling conventional coin batteries with customized beaker batteries to pinpoint the operating mechanism of Zn−MnO2 batteries. This approach visually simulates the operating state of batteries in different scenarios and allows for a comprehensive study of the operating mechanism of aqueous Zn−MnO2 batteries under mild acidic conditions. It is validated that the electrochemical performance can be modulated by controlling the addition of Mn2+ to the electrolyte. The method is utilized to systematically eliminate the possibility of Zn2+ and/or H+ intercalation/de‐intercalation reactions, thereby confirming the dominance of the MnO2/Mn2+ dissolution‐deposition mechanism. By combining a series of phase and spectroscopic characterizations, the compositional, morphological and structural evolution of electrodes and electrolytes during battery cycling is probed, elucidating the intrinsic battery chemistry of MnO2 in mild acid electrolytes. Such a methodology developed can be extended to other energy storage systems, providing a universal approach to accurately identify the reaction mechanism of aqueous aluminum‐ion batteries as well. [ABSTRACT FROM AUTHOR]

Developing cost‐effective and sustainable acidic water oxidation catalysts requires significant advances in material design and in‐depth mechanism understanding for proton exchange membrane water electrolysis. Herein, we developed a single atom regulatory strategy to construct Co−Co dinuclear active sites (DASs) catalysts that atomically dispersed zirconium doped Co9S8/Co3O4 heterostructure. The X‐ray absorption fine structure elucidated the incorporation of Zr greatly facilitated the generation of Co−Co DASs layer with stretching of cobalt oxygen bond and S−Co−O heterogeneous grain boundaries interfaces, engineering attractive activity of significantly reduced overpotential of 75 mV at 10 mA cm−2, a breakthrough of 500 mA cm−2 high current density, and water splitting stability of 500 hours in acid, making it one of the best‐performing acid‐stable OER non‐noble metal materials. The optimized catalyst with interatomic Co−Co distance (ca. 2.80 Å) followed oxo‐oxo coupling mechanism that involved obvious oxygen bridges on dinuclear Co sites (1,090 cm−1), confirmed by in situ SR‐FTIR, XAFS and theoretical simulations. Furthermore, a major breakthrough of 120,000 mA g−1 high mass current density using the first reported noble metal‐free cobalt anode catalyst of Co−Co DASs/ZCC in PEM‐WE at 2.14 V was recorded. [ABSTRACT FROM AUTHOR]

Water electrolysis for H2 production is restricted by the sluggish oxygen evolution reaction (OER). Using the thermodynamically more favorable hydrazine oxidation reaction (HzOR) to replace OER has attracted ever‐growing attention. Herein, we report a twisted NiCoP nanowire array immobilized with Ru single atoms (Ru1−NiCoP) as superior bifunctional electrocatalyst toward both HzOR and hydrogen evolution reaction (HER), realizing an ultralow working potential of −60 mV and overpotential of 32 mV for a current density of 10 mA cm−2, respectively. Inspiringly, two‐electrode electrolyzer based on overall hydrazine splitting (OHzS) demonstrates outstanding activity with a record‐high current density of 522 mA cm−2 at cell voltage of 0.3 V. DFT calculations elucidate the cooperative Ni(Co)−Ru−P sites in Ru1−NiCoP optimize H* adsorption, and enhance adsorption of *N2H2 to significantly lower the energy barrier for hydrazine dehydrogenation. Moreover, a self‐powered H2 production system utilizing OHzS device driven by direct hydrazine fuel cell (DHzFC) achieve a satisfactory rate of 24.0 mol h−1 m−2. [ABSTRACT FROM AUTHOR]

Metal‐nitrogen‐carbon catalysts, as promising alternative to platinum‐based catalysts for oxygen reduction reaction (ORR), are still highly expected to achieve better performance by modulating the composition and spatial structure of active site. Herein, we constructed the non‐planar nest‐like [Fe2S2] cluster sites in N‐doped carbon plane. Adjacent double Fe atoms effectively weaken the O−O bond by forming a peroxide bridge‐like adsorption configuration, and the introduction of S atoms breaks the planar coordination of Fe resulting in greater structural deformation tension, lower spin state, and downward shifted Fe d‐band center, which together facilitate the release of OH* intermediate. Hence, the non‐planar [Fe2S2] cluster catalyst, with a half‐wave potential of 0.92 V, displays superior ORR activity than that of planar [FeN4] or [Fe2N6]. This work provides insights into the co‐regulation of atomic composition and spatial configuration for efficient oxygen reduction catalysis. [ABSTRACT FROM AUTHOR]

Fine‐tuning single‐atom catalysts (SACs) to surpass their activity limit remains challenging at their atomic scale. Herein, we exploit p‐type semiconducting character of SACs having a metal center coordinated to nitrogen donors (MeNx) and rectify their local charge density by an n‐type semiconductor support. With iron phthalocyanine (FePc) as a model SAC, introducing an n‐type gallium monosulfide that features a low work function generates a space‐charged region across the junction interface, and causes distortion of the FeN4 moiety and spin‐state transition in the FeII center. This catalyst shows an over two‐fold higher specific oxygen‐reduction activity than that of pristine FePc. We further employ three other n‐type metal chalcogenides of varying work function as supports, and discover a linear correlation between the activities of the supported FeN4 and the rectification degrees, which clearly indicates that SACs can be continuously tuned by this rectification strategy. [ABSTRACT FROM AUTHOR]

Photoreduction of CO2 into solar fuels has received great interest, but suffers from low catalytic efficiency and poor selectivity. Herein, two single‐Cu‐atom catalysts with unique Cu configurations in phosphorus‐doped carbon nitride (PCN), namely, Cu1N3@PCN and Cu1P3@PCN were fabricated via selective phosphidation, and tested in visible light‐driven CO2 reduction by H2O without sacrificial agents. Cu1N3@PCN was exclusively active for CO production with a rate of 49.8 μmolCO gcat−1 h−1, outperforming most polymeric carbon nitride (C3N4) based catalysts, while Cu1P3@PCN preferably yielded H2. Experimental and theoretical analysis suggested that doping P in C3N4 by replacing a corner C atom upshifted the d‐band center of Cu in Cu1N3@PCN close to the Fermi level, which boosted the adsorption and activation of CO2 on Cu1N3, making Cu1N3@PCN efficiently convert CO2 to CO. In contrast, Cu1P3@PCN with a much lower Cu 3d electron energy exhibited negligible CO2 adsorption, thereby preferring H2 formation via photocatalytic H2O splitting. [ABSTRACT FROM AUTHOR]

Single‐atom active‐site catalysts have attracted significant attention in the field of photocatalytic CO2 conversion. However, designing active sites for CO2 reduction and H2O oxidation simultaneously on a photocatalyst and combining the corresponding half‐reaction in a photocatalytic system is still difficult. Here, we synthesized a bimetallic single‐atom active‐site photocatalyst with two compatible active centers of Mn and Co on carbon nitride (Mn1Co1/CN). Our experimental results and density functional theory calculations showed that the active center of Mn promotes H2O oxidation by accumulating photogenerated holes. In addition, the active center of Co promotes CO2 activation by increasing the bond length and bond angle of CO2 molecules. Benefiting from the synergistic effect of the atomic active centers, the synthesized Mn1Co1/CN exhibited a CO production rate of 47 μmol g−1 h−1, which is significantly higher than that of the corresponding single‐metal active‐site photocatalyst. [ABSTRACT FROM AUTHOR]

The development of highly active and stable bifunctional noble‐metal‐based electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is a crucial goal for clean and renewable energy, which still remains challenging. Herein, we report an efficient and stable catalyst comprising a Co single atom incorporated in an RuO2 sphere for HER and OER, in which the Co single atom in the RuO2 sphere was confirmed by XAS, AC‐STEM, and DFT. This tailoring strategy uses a Co single atom to modify the electronic structures of the surrounding Ru atoms and thereby remarkably elevates the electrocatalytic activities. The catalyst requires ultralow overpotentials, 45 mV for HER and 200 mV for OER, to deliver a current density of 10 mA cm−2. The theoretical calculations reveal that the energy barriers for HER and OER are lowered after incorporation of a cobalt single atom. [ABSTRACT FROM AUTHOR]

The exploitation of highly efficient carbon dioxide reduction (CO2RR) electrocatalyst for methane (CH4) electrosynthesis has attracted great attention for the intermittent renewable electricity storage but remains challenging. Here, N‐heterocyclic carbene (NHC)‐ligated copper single atom site (Cu SAS) embedded in metal–organic framework is reported (2Bn‐Cu@UiO‐67), which can achieve an outstanding Faradaic efficiency (FE) of 81 % for the CO2 reduction to CH4 at −1.5 V vs. RHE with a current density of 420 mA cm−2. The CH4 FE of our catalyst remains above 70 % within a wide potential range and achieves an unprecedented turnover frequency (TOF) of 16.3 s−1. The σ donation of NHC enriches the surface electron density of Cu SAS and promotes the preferential adsorption of CHO* intermediates. The porosity of the catalyst facilitates the diffusion of CO2 to 2Bn‐Cu, significantly increasing the availability of each catalytic center. [ABSTRACT FROM AUTHOR]

Electrochemical reduction of carbon dioxide (CO2) into chemicals and fuels has recently attracted much interest, but normally suffers from a high overpotential and low selectivity. In this work, single P atoms were introduced into a N‐doped carbon supported single Fe atom catalyst (Fe‐SAC/NPC) mainly in the form of P−C bonds for CO2 electroreduction to CO in an aqueous solution. This catalyst exhibited a CO Faradaic efficiency of ≈97 % at a low overpotential of 320 mV, and a Tafel slope of only 59 mV dec−1, comparable to state‐of‐the‐art gold catalysts. Experimental analysis combined with DFT calculations suggested that single P atom in high coordination shells (n≥3), in particular the third coordination shell of Fe center enhanced the electronic localization of Fe, which improved the stabilization of the key *COOH intermediate on Fe, leading to superior CO2 electrochemical reduction performance at low overpotentials. [ABSTRACT FROM AUTHOR]

Dual‐atom site catalysts (DACs) have emerged as a new frontier in heterogeneous catalysis because the synergistic effect between adjacent metal atoms can promote their catalytic activity while maintaining the advantages of single‐atom site catalysts (SACs), like 100 % atomic utilization efficiency and excellent selectivity. Herein, a supported Pd2 DAC was synthesized and used for electrochemical CO2 reduction reaction (CO2RR) for the first time. The as‐obtained Pd2 DAC exhibited superior CO2RR catalytic performance with 98.2 % CO faradic efficiency at −0.85 V vs. RHE, far exceeding that of Pd1 SAC, and coupled with long‐term stability. The density functional theory (DFT) calculations revealed that the intrinsic reason for the superior activity of Pd2 DAC toward CO2RR was the electron transfer between Pd atoms at the dimeric Pd sites. Thus, Pd2 DAC possessed moderate adsorption strength of CO*, which was beneficial for CO production in CO2RR. [ABSTRACT FROM AUTHOR]

We report an Ag1 single‐atom catalyst (Ag1/MnO2), which was synthesized from thermal transformation of Ag nanoparticles (NPs) and surface reconstruction of MnO2. The evolution process of Ag NPs to single atoms is firstly revealed by various techniques, including in situ ETEM, in situ XRD and DFT calculations. The temperature‐induced surface reconstruction process from the MnO2 (211) to (310) lattice plane is critical to firmly confine the existing surface of Ag single atoms; that is, the thermal treatment and surface reconstruction of MnO2 is the driving force for the formation of single Ag atoms. The as‐obtained Ag1/MnO2 achieved 95.7 % Faradic efficiency at −0.85 V vs. RHE, and coupled with long‐term stability for electrochemical CO2 reduction reaction (CO2RR). DFT calculations indicated single Ag sites possessed high electronic density close to Fermi Level and could act exclusively as the active sites in the CO2RR. As a result, the Ag1/MnO2 catalyst demonstrated remarkable performance for the CO2RR, far surpassing the conventional Ag nanosized catalyst (AgNP/MnO2) and other reported Ag‐based catalysts. [ABSTRACT FROM AUTHOR]

Demonstrated here is the correlation between atomic configuration induced electronic density of single‐atom Co active sites and oxygen reduction reaction (ORR) performance by combining density‐functional theory (DFT) calculations and electrochemical analysis. Guided by DFT calculations, a MOF‐derived Co single‐atom catalyst with the optimal Co1‐N3PS active moiety incorporated in a hollow carbon polyhedron (Co1‐N3PS/HC) was designed and synthesized. Co1‐N3PS/HC exhibits outstanding alkaline ORR activity with a half‐wave potential of 0.920 V and superior ORR kinetics with record‐level kinetic current density and an ultralow Tafel slope of 31 mV dec−1, exceeding that of Pt/C and almost all non‐precious ORR electrocatalysts. In acidic media the ORR kinetics of Co1‐N3PS/HC still surpasses that of Pt/C. This work offers atomic‐level insight into the relationship between electronic density of the active site and catalytic properties, promoting rational design of efficient catalysts. [ABSTRACT FROM AUTHOR]

Main‐group element indium (In) is a promising electrocatalyst which triggers CO2 reduction to formate, while the high overpotential and low Faradaic efficiency (FE) hinder its practical application. Herein, we rationally design a new In single‐atom catalyst containing exclusive isolated Inδ+–N4 atomic interface sites for CO2 electroreduction to formate with high efficiency. This catalyst exhibits an extremely large turnover frequency (TOF) up to 12500 h−1 at −0.95 V versus the reversible hydrogen electrode (RHE), with a FE for formate of 96 % and current density of 8.87 mA cm−2 at low potential of −0.65 V versus RHE. Our findings present a feasible strategy for the accurate regulation of main‐group indium catalysts for CO2 reduction at atomic scale. [ABSTRACT FROM AUTHOR]