Asymmetric Local Electric Field Induced by Dual Heteroatoms on Copper Boosts Efficient CO2 Reduction Over Ultrawide Potential Window.

Electrocatalytic reduction of CO2 powered by renewable electricity provides an elegant route for converting CO2 into valuable chemicals and feedstocks, but normally suffers from a high overpotential and low selectivity. Herein, Ag and Sn heteroatoms were simultaneously introduced into nanoporous Cu (np-Ag/Sn-Cu) mainly in the form of an asymmetric local electric field for CO2 electroreduction to CO in an aqueous solution. The designed np-Ag/Sn-Cu catalyst realizes a recorded 90% energy efficiency and a 100% CO Faradaic efficiency over ultrawide potential window (ΔE = 1.4 V), outperforming state-of-the-art Au and Ag-based catalysts. Density functional theory calculations combined with in situ spectroscopy studies reveal that Ag and Sn heteroatoms incorporated into Cu matrix could generate strong and asymmetric local electric field, which promotes the activation of CO2 molecules, enhances the stabilization of the *COOH intermediate, and suppresses the hydrogen evolution reaction, thus favoring the production of CO during CO2RR.

Atomically dispersed low-valent Au boosts photocatalytic hydroxyl radical production.

Providing affordable, safe drinking water and universal sanitation poses a grand societal challenge. Here we developed atomically dispersed Au on potassium-incorporated polymeric carbon nitride material that could simultaneously boost photocatalytic generation of ·OH and H2O2 with an apparent quantum efficiency over 85% at 420 nm. Potassium introduction into the poly(heptazine imide) matrix formed strong K-N bonds and rendered Au with an oxidation number close to 0. Extensive experimental characterization and computational simulations revealed that the low-valent Au altered the materials' band structure to trap highly localized holes produced under photoexcitation. These highly localized holes could boost the 1e- water oxidation reaction to form highly oxidative ·OH and simultaneously dissociate the hydrogen atom in H2O, which greatly promoted the reduction of oxygen to H2O2. The photogenerated ·OH led to an efficiency enhancement for visible-light-response superhydrophilicity. Furthermore, photo-illumination in an onsite fixed-bed reactor could disinfect water at a rate of 66 L H2O m-2 per day.

Coupling Nano and Atomic Electric Field Confinement for Robust Alkaline Oxygen Evolution.

The alkaline oxygen evolution reaction (OER) is a promising avenue for producing clean fuels and storing intermittent energy. However, challenges such as excessive OH- consumption and strong adsorption of oxygen-containing intermediates hinder the development of alkaline OER. In this study, we propose a cooperative strategy by leveraging both nano-scale and atomically local electric fields for alkaline OER, demonstrated through the synthesis of Mn single atom doped CoP nanoneedles (Mn SA-CoP NNs). Finite element method simulations and density functional theory calculations predict that the nano-scale local electric field enriches OH- around the catalyst surface, while the atomically local electric field improves *O desorption. Experimental validation using in situ attenuated total reflection infrared and Raman spectroscopy confirms the effectiveness of the nano-scale and atomically electric fields. Mn SA-CoP NNs exhibit an ultra-low overpotential of 189 mV at 10 mA cm-2 and stable operation over 100 hours at ~100 mA cm-2 during alkaline OER. This innovative strategy provides new insights for enhancing catalyst performance in energy conversion reactions.

Platinum-Ruthenium Dual-Atomic Sites Dispersed in Nanoporous Ni0.85Se Enabling Ampere-Level Current Density Hydrogen Production.

Alkaline anion-exchange-membrane water electrolyzers (AEMWEs) using earth-abundant catalysts is a promising approach for the generation of green H2. However, the AEMWEs with alkaline electrolytes suffer from poor performance at high current density compared to proton exchange membrane electrolyzers. Here, atomically dispersed Pt-Ru dual sites co-embedded in nanoporous nickel selenides (np/Pt1Ru1-Ni0.85Se) are developed by a rapid melt-quenching approach to achieve highly-efficient alkaline hydrogen evolution reaction. The np/Pt1Ru1-Ni0.85Se catalyst shows ampere-level current density with a low overpotential (46 mV at 10 mA cm-2 and 225 mV at 1000 mA cm-2), low Tafel slope (32.4 mV dec-1), and excellent long-term durability, significantly outperforming the benchmark Pt/C catalyst and other advanced large-current catalysts. The remarkable HER performance of nanoporous Pt1Ru1-Ni0.85Se is attributed to the strong intracrystal electronic metal-support interaction (IEMSI) between Pt-Se-Ru sites and Ni0.85Se support which can greatly enlarge the charge redistribution density, reduce the energy barrier of water dissociation, and optimize the potential determining step. Furthermore, the assembled alkaline AEMWE with an ultralow Pt and Ru loading realizes an industrial-level current density of 1 A cm-2 at 1.84 volts with high durability.

Constructing Nanoporous Ir/Ta2 O5 Interfaces on Metallic Glass for Durable Acidic Water Oxidation.

Although proton exchange membrane water electrolyzers (PEMWE) are considered as a promising technique for green hydrogen production, it remains crucial to develop intrinsically effective oxygen evolution reaction (OER) electrocatalysts with high activity and durability. Here, a flexible self-supporting electrode with nanoporous Ir/Ta2O5 electroactive surface is reported for acidic OER via dealloying IrTaCoB metallic glass ribbons. The catalyst exhibits excellent electrocatalytic OER performance with an overpotential of 218 mV for a current density of 10 mA cm-2 and a small Tafel slope of 46.1 mV dec-1 in acidic media, superior to most electrocatalysts. More impressively, the assembled PEMWE with nanoporous Ir/Ta2 O5 as an anode shows exceptional performance of electrocatalytic hydrogen production and can operate steadily for 260 h at 100 mA cm-2 . In situ spectroscopy characterizations and density functional theory calculations reveal that the modest adsorption of OOH* intermediates to active Ir sites lower the OER energy barrier, while the electron donation behavior of Ta2 O5 to stabilize the high-valence states of Ir during the OER process extended catalyst's durability.

Potential Alignment in Tandem Catalysts Enhances CO2-to-C2H4 Conversion Efficiencies.

The in-tandem catalyst holds great promise for addressing the limitation of low *CO coverage on Cu-based materials for selective C2H4 generation during CO2 electroreduction. However, the potential mismatch between the CO-formation catalyst and the favorable C-C coupling Cu catalyst represents a bottleneck in these types of electrocatalysts, resulting in low tandem efficiencies. In this study, we propose a robust solution to this problem by introducing a wide-CO generation-potential window nickel single atom catalyst (Ni SAC) supported on a Cu catalyst. The selection of Ni SAC was based on theoretical calculations, and its excellent performance was further confirmed by using in situ IR spectroscopy. The facilitated carbon dimerization in our tandem catalyst led to a ∼370 mA/cm2 partial current density of C2H4, corresponding to a faradic efficiency of ∼62%. This performance remained stable and consistent for at least ∼14 h at a high current density of 500 mA/cm2 in a flow-cell reactor, outperforming most tandem catalysts reported so far.

Elemental Sulfur and Organic Matter Amendment Drive Alkaline pH Neutralization and Mineral Weathering in Iron Ore Tailings Through Inducing Sulfur Oxidizing Bacteria.

Mineral weathering and alkaline pH neutralization are prerequisites to the ecoengineering of alkaline Fe-ore tailings into soil-like growth media (i.e., Technosols). These processes can be accelerated by the growth and physiological functions of tolerant sulfur oxidizing bacteria (SOB) in tailings. The present study characterized an indigenous SOB community enriched in the tailings, in response to the addition of elemental sulfur (S0) and organic matter (OM), as well as resultant S0oxidation, pH neutralization, and mineral weathering in a glasshouse experiment. The addition of S0 was found to have stimulated the growth of indigenous SOB, such as acidophilic Alicyclobacillaceae, Bacillaceae, and Hydrogenophilaceae in tailings. The OM amendment favored the growth of heterotrophic/mixotrophic SOB (e.g., class Alphaproteobacteria and Gammaproteobacteria). The resultant S0 oxidation neutralized the alkaline pH and enhanced the weathering of biotite-like minerals and formation of secondary minerals, such as ferrihydrite- and jarosite-like minerals. The improved physicochemical properties and secondary mineral formation facilitated organo-mineral associations that are critical to soil aggregate formation. From these findings, co-amendments of S0 and plant biomass (OM) can be applied to enhance the abundance of the indigenous SOB community in tailings and accelerate mineral weathering and geochemical changes for eco-engineered soil formation, as a sustainable option for rehabilitation of Fe ore tailings.

Stabilizing ruthenium dioxide with cation-anchored sulfate for durable oxygen evolution in proton-exchange membrane water electrolyzers.

Ruthenium dioxide is the most promising alternative to the prevailing but expensive iridium-based catalysts for the oxygen evolution reaction in proton-exchange membrane water electrolyzers. However, the under-coordinated lattice oxygen of ruthenium dioxide is prone to over-oxidation, and oxygen vacancies are formed at high oxidation potentials under acidic corrosive conditions. Consequently, ruthenium atoms adjacent to oxygen vacancies are oxidized into soluble high-valence derivatives, causing the collapse of the ruthenium dioxide crystal structure and leading to its poor stability. Here, we report an oxyanion protection strategy to prevent the formation of oxygen vacancies on the ruthenium dioxide surface by forming coordination-saturated lattice oxygen. Combining density functional theory calculations, electrochemical measurements, and a suite of operando spectroscopies, we showcase that barium-anchored sulfate can greatly impede ruthenium loss and extend the lifetime of ruthenium-based catalysts during acidic oxygen evolution, while maintaining the activity. This work paves a new way for designing stable and active anode catalysts toward acidic water splitting.

Sulfur-Stabilizing Ultrafine High-Entropy Alloy Nanoparticles on MXene for Highly Efficient Ethanol Electrooxidation.

High-entropy alloys (HEAs) are significantly promising candidates for heterogeneous catalysis, yet the controllable synthesis of ultrafine HEA nanoparticles (NPs) remains a formidable challenge due to severe thermal sintering during the high-temperature fabrication process. Herein, we report a sulfur-stabilizing strategy to construct ultrafine HEA NPs with an average diameter of 4.02 nm supported on sulfur-modified Ti3C2Tx (S-Ti3C2Tx) MXene, on which the strong interfacial metal-sulfur interactions between HEA NPs and the S-Ti3C2Tx supports significantly increase the interfacial adhesion strength, thus greatly suppressing nanoparticle sintering by retarding both particle migration and metal atom diffusion. The representative quinary PtPdCuNiCo HEA-S-Ti3C2Tx exhibits excellent catalytic performance toward alkaline ethanol oxidation reaction (EOR) with an ultrahigh mass activity of 7.03 A mgPt+Pd-1, which is 4.34 and 5.17 times higher than those of the commercial Pt/C and Pd/C catalysts, respectively. In situ attenuated total reflection-infrared spectroscopy studies reveal that the high intrinsic catalytic activity for the EOR can be ascribed to the synergy of different catalytically active sites of HEA NPs and the well-designed interfacial metal-sulfur interactions.

Operando Mössbauer Spectroscopic Tracking the Metastable State of Atomically Dispersed Tin in Copper Oxide for Selective CO2 Electroreduction.

Metastable state is the most active catalyst state that dictates the overall catalytic performance and rules of catalytic behaviors; however, identification and stabilization of the metastable state of catalyst are still highly challenging due to the continuous evolution of catalytic sites during the reaction process. In this work, operando 119Sn Mössbauer measurements and theoretical simulations were performed to track and identify the metastable state of single-atom Sn in copper oxide (Sn1-CuO) for highly selective CO2 electroreduction to CO. A maximum CO Faradaic efficiency of around 98% at -0.8 V (vs. RHE) over Sn1-CuO was achieved at an optimized Sn loading of 5.25 wt. %. Operando Mössbauer spectroscopy clearly identified the dynamic evolution of atomically dispersed Sn4+ sites in the CuO matrix that enabled the in situ transformation of Sn4+-O4-Cu2+ to a metastable state Sn4+-O3-Cu+ under CO2RR conditions. In combination with quasi in situ X-ray photoelectron spectroscopy, operando Raman and attenuated total reflectance surface enhanced infrared absorption spectroscopies, the promoted desorption of *CO over the Sn4+-O3 stabilized adjacent Cu+ site was evidenced. In addition, density functional theory calculations further verified that the in situ construction of Sn4+-O3-Cu+ as the true catalytic site altered the reaction path via modifying the adsorption configuration of the *COOH intermediate, which effectively reduced the reaction free energy required for the hydrogenation of CO2 and the desorption of the *CO, thereby greatly facilitating the CO2-to-CO conversion. This work provides a fundamental insight into the role of single Sn atoms on in situ tuning the electronic structure of Cu-based catalysts, which may pave the way for the development of efficient catalysts for high-selectivity CO2 electroreduction.

Temperature-Dependent Structures of Single-Atom Catalysts.

Single-atom catalysts (SACs) have the unique coordination environment and electronic structure due to the quantum size effect, which plays an essential role in facilitating catalytic reactions. However, due to the limited understanding of the formation mechanism of single atoms, achieving the modulation of the local atomic structure of SACs is still difficult and challenging. Herein, we have prepared a series of Ni SACs loaded on nitrogen-doped carbon substrates with different parameters using a dissolution-and-carbonization method to systematically investigate the effect of temperature on the structure of the SACs. The results of characterization and electrochemical measurements are analyzed to reveal the uniform law between temperature and the metal loading, bond length, coordination number, valence state and CO2 reduction performance, showing the feasibility of controlling the structure of SACs through temperature to regulate the catalytic performance. This is important for the understanding of catalytic reaction mechanisms and the design of efficient catalysts.

Dealloying-Induced Zeolite-like Metal Framework of AB2 Laves Phase Intermetallic Electrocatalysts.

Exploring an efficient and robust electrocatalyst for hydrogen evolution reaction (HER) at high pH and temperature holds the key to the industrial application of alkaline water electrolysis (AWE). Herein, we design an open tunnel structure by dealloying a series of Laves phase intermetallics, i.e., MCo2 and MRu0.25Co1.75 (M = Sc and Zr). The dealloying process can induce a zeolite-like metal framework for ScCo2 and ScRu0.25Co1.75 by stripping Sc metal from the center of a tunnel structure. This structural engineering significantly lowers their overpotentials at a current density of 500 mA/cm2 (η500) ca. 80 mV in 1.0 M KOH. Through a simple process, ScRu0.25Co1.75 can be easily decorated on a carbon cloth substrate and only requires 132 mV to reach 500 mA/cm2. More importantly it can maintain activity over 1000 h in industrial conditions (6.0 M KOH at 333 K), showing its potential for practical industrial applications.

Ecological engineering of iron ore tailings into useable soils for sustainable rehabilitation.

Ecological engineering of soil formation in tailings is an emerging technology toward sustainable rehabilitation of iron (Fe) ore tailings landscapes worldwide, which requires the formation of well-organized and stable soil aggregates in finely textured tailings. Here, we demonstrate an approach using microbial and rhizosphere processes to progressively drive aggregate formation and development in Fe ore tailings. The aggregates were initially formed through the agglomeration of mineral particles by organic cements derived from microbial decomposition of exogenous organic matter. The aggregate stability was consolidated by colloidal nanosized Fe(III)-Si minerals formed during Fe-bearing primary mineral weathering driven by rhizosphere biogeochemical processes of pioneer plants. From these findings, we proposed a conceptual model for progressive aggregate structure development in the tailings with Fe(III)-Si rich cements as core nuclei. This renewable resource dependent eco-engineering approach opens a sustainable pathway to achieve resilient tailings rehabilitation without resorting to excavating natural soil resources.

Unraveling the Electronic Structure and Dynamics of the Atomically Dispersed Iron Sites in Electrochemical CO2 Reduction.

Single-atom catalysts with a well-defined metal center open unique opportunities for exploring the catalytically active site and reaction mechanism of chemical reactions. However, understanding of the electronic and structural dynamics of single-atom catalytic centers under reaction conditions is still limited due to the challenge of combining operando techniques that are sensitive to such sites and model single-atom systems. Herein, supported by state-of-the-art operando techniques, we provide an in-depth study of the dynamic structural and electronic evolution during the electrochemical CO2 reduction reaction (CO2RR) of a model catalyst comprising iron only as a high-spin (HS) Fe(III)N4 center in its resting state. Operando 57Fe Mössbauer and X-ray absorption spectroscopies clearly evidence the change from a HS Fe(III)N4 to a HS Fe(II)N4 center with decreasing potential, CO2- or Ar-saturation of the electrolyte, leading to different adsorbates and stability of the HS Fe(II)N4 center. With operando Raman spectroscopy and cyclic voltammetry, we identify that the phthalocyanine (Pc) ligand coordinating the iron cation center undergoes a redox process from Fe(II)Pc to Fe(II)Pc-. Altogether, the HS Fe(II)Pc- species is identified as the catalytic intermediate for CO2RR. Furthermore, theoretical calculations reveal that the electroreduction of the Pc ligand modifies the d-band center of the in situ generated HS Fe(II)Pc- species, resulting in an optimal binding strength to CO2 and thus boosting the catalytic performance of CO2RR. This work provides both experimental and theoretical evidence toward the electronic structural and dynamics of reactive sites in single-Fe-atom materials and shall guide the design of novel efficient catalysts for CO2RR.

Efficient electrosynthesis of formamide from carbon monoxide and nitrite on a Ru-dispersed Cu nanocluster catalyst.

Conversion into high-value-added organic nitrogen compounds through electrochemical C-N coupling reactions under ambient conditions is regarded as a sustainable development strategy to achieve carbon neutrality and high-value utilization of harmful substances. Herein, we report an electrochemical process for selective synthesis of high-valued formamide from carbon monoxide and nitrite with a Ru1Cu single-atom alloy under ambient conditions, which achieves a high formamide selectivity with Faradaic efficiency of 45.65 ± 0.76% at -0.5 V vs. RHE. In situ X-ray absorption spectroscopy, coupled with in situ Raman spectroscopy and density functional theory calculations results reveal that the adjacent Ru-Cu dual active sites can spontaneously couple *CO and *NH2 intermediates to realize a critical C-N coupling reaction, enabling high-performance electrosynthesis of formamide. This work offers insight into the high-value formamide electrocatalysis through coupling CO and NO2- under ambient conditions, paving the way for the synthesis of more-sustainable and high-value chemical products.

Palladium metallene confined on MXene with increased hydroxyl binding strength for highly efficient ethanol electrooxidation.

Rational design and synthesis of high-performance electrocatalysts for ethanol oxidation reaction (EOR) is crucial to large-scale commercialization of direct ethanol fuel cells, but it is still an incredible challenge. Herein, a unique Pd metallene/Ti3C2Tx MXene (Pdene/Ti3C2Tx)-supported electrocatalyst is constructed via an in-situ growth approach for high-efficiency EOR. The resulting Pdene/Ti3C2Tx catalyst achieves an ultrahigh mass activity of 7.47 A mgPd-1 under alkaline condition, as well as high tolerance to CO poisoning. In situ attenuated total reflection-infrared spectroscopy studies combined with density functional theory calculations reveal that the excellent EOR activity of Pdene/Ti3C2Tx catalyst is attributed to the unique and stable interfaces which reduce the reaction energy barrier of *CH3CO intermediate oxidation and facilitate oxidative removal of CO poisonous species by increasing the Pd-OH binding strength.

Ferromagnetic single-atom spin catalyst for boosting water splitting.

Heterogeneous single-atom spin catalysts combined with magnetic fields provide a powerful means for accelerating chemical reactions with enhanced metal utilization and reaction efficiency. However, designing these catalysts remains challenging due to the need for a high density of atomically dispersed active sites with a short-range quantum spin exchange interaction and long-range ferromagnetic ordering. Here, we devised a scalable hydrothermal approach involving an operando acidic environment for synthesizing various single-atom spin catalysts with widely tunable substitutional magnetic atoms (M1) in a MoS2 host. Among all the M1/MoS2 species, Ni1/MoS2 adopts a distorted tetragonal structure that prompts both ferromagnetic coupling to nearby S atoms as well as adjacent Ni1 sites, resulting in global room-temperature ferromagnetism. Such coupling benefits spin-selective charge transfer in oxygen evolution reactions to produce triplet O2. Furthermore, a mild magnetic field of ~0.5 T enhances the oxygen evolution reaction magnetocurrent by ~2,880% over Ni1/MoS2, leading to excellent activity and stability in both seawater and pure water splitting cells. As supported by operando characterizations and theoretical calculations, a great magnetic-field-enhanced oxygen evolution reaction performance over Ni1/MoS2 is attributed to a field-induced spin alignment and spin density optimization over S active sites arising from field-regulated S(p)-Ni(d) hybridization, which in turn optimizes the adsorption energies for radical intermediates to reduce overall reaction barriers.

Asymmetric Coordination Induces Electron Localization at Ca Sites for Robust CO2 Electroreduction to CO.

Main group single atom catalysts (SACs) are promising for CO2 electroreduction to CO by virtue of their ability in preventing the hydrogen evolution reaction and CO poisoning. Unfortunately, their delocalized orbitals reduce the CO2 activation to *COOH. Herein, an O doping strategy to localize electrons on p-orbitals through asymmetric coordination of Ca SAC sites (Ca-N3 O) is developed, thus enhancing the CO2 activation. Theoretical calculations indicate that asymmetric coordination of Ca-N3 O improves electron-localization around Ca sites and thus promotes *COOH formation. X-ray absorption fine spectroscopy shows the obtained Ca-N3 O features: one O and three N coordinated atoms with one Ca as a reactive site. In situ attenuated total reflection infrared spectroscopy proves that Ca-N3 O promotes *COOH formation. As a result, the Ca-N3 O catalyst exhibits a state-of-the-art turnover frequency of ≈15 000 per hour in an H-cell and a large current density of -400 mA cm-2 with a CO Faradaic efficiency (FE) ≥ 90% in a flow cell. Moreover, Ca-N3 O sites retain a FE above 90% even with a 30% diluted CO2 concentration.

Mineral weathering of iron ore tailings primed by Acidithiobacillus ferrooxidans and elemental sulfur under contrasting pH conditions.

The acidophilic sulfur oxidizing bacterium (SOB), Acidithiobacillus ferrooxidans, has been found to stimulate elemental sulfur (S0) oxidation and mineral weathering in alkaline Fe ore tailings. However, A. ferrooxidans growth and activities depend on the pH conditions surrounding their interfaces with minerals. The present study aimed to investigate how pH influences bacterial growth and functions in Fe ore tailings. A simulated aquatic 'homogeneous' incubation system was initially adjusted into acidic (pH 4), neutral (pH 7) and alkaline (pH 9) conditions, which mimicked the microenvironmental conditions of the water-cell-mineral interfaces in the tailings. It was found that A. ferrooxidans grew well and oxidised S0 under the prevailing and initially acidic conditions (pH < 6). These stimulated the weathering of biotite and amphibole-like minerals and the formation of nanosized jarosite and ferrihydrite-like minerals mediated by extracellular polymer substrate (EPS). In contrast, the initially neutral/alkaline pH conditions (i.e., pH > 7) with the presence of the alkaline tailings restricted SOB growth and functions in S0-oxidation and mineral weathering. These findings suggest that it is essential to prime acidic conditions in microenvironments to support SOB growth, activities, and functions toward mineral weathering in tailings, providing critical basis for involving SOB in eco-engineered pedogenesis in tailings.

Rapid Melt-Quenching Enables General Synthesis of High-Loading Single-Atom Catalysts with Bicontinuous Nanoporous Structure.

Single-atom catalysts have attracted extensive attention due to their unique atomic structures and extraordinary activities in catalyzing chemical reactions. However, the lack of general and efficient approaches for producing high-density single atoms on suitably tailored supporting matrixes hinders their industrial applications. Here, a rapid melt-quenching strategy with high throughput to synthesize single atoms with high metal-atom loadings of up to 9.7 wt% or 2.6 at% on nanoporous metal compounds is reported, representing several-fold improvements compared to benchmarks in the literature. Mechanism characterizations reveal that the high-temperature melting provides the essential liquid environment and activation energy to achieve the atomization of metals, while the following rapid-quenching pins the isolated metal atoms and stabilizes the coordination environment. In comparison with carbon-supported single-atom catalysts, various collaboration combinations of single atoms and nanoporous metal compounds can be synthesized using the strategy, thus achieving efficient hydrazine oxidation-assisted H2 production. This synthesis protocol is highly compatible with automatic operation, which provides a feasible and general route to design and manufacture specific single-atom catalysts with tunable atomic metal components and supporting matrixes, thus promoting the deployment of single-atom catalysts for various energy technology applications.