Phosphorus Coordination in Second Shell of Single-Atom Cu Catalyst toward Acetate Production in CO Electroreduction.

It is challenging to achieve highly efficient CO-CO coupling toward C2 products in electrochemical CO and CO2 reductions on single-atom catalysts (SACs). Herein, we report a modulation strategy of phosphorus coordination in the second shell of Cu SACs with a Cu-N4 structure (Cu-N4-P4/C4) and demonstrate experimentally and theoretically the CO-CO coupling through an Eley-Rideal mechanism in electrochemical CO reduction (COR). Remarkably, the Cu SACs exhibit a selectivity of 63.9% toward acetate production in alkaline media on a gas diffusion electrode. Operando synchrotron-based X-ray absorption spectroscopy confirms the robust Cu-N4-P4/C4 structure of the Cu SACs against the harsh electrochemical reduction conditions throughout the electrochemical COR, instead of forming Cu clusters for Cu-N4 configuration, enabling an excellent COR performance toward acetate. This work not only unravels a new mechanism for CO-CO coupling toward C2 products in COR but also offers a novel strategy for SAC regulation toward multicarbon production with high activity, selectivity, and durability.

Identifying an Interfacial Stabilizer for Regeneration-Free 300 h Electrochemical CO2 Reduction to C2 Products.

The electrochemical CO2 reduction reaction (CO2RR) to produce high value-added hydrocarbons and oxygenates presents a sustainable and compelling approach toward a carbon-neutral society. However, uncontrollable migration of active sites during the electrochemical CO2RR limits its catalytic ability to simultaneously achieve high C2 selectivity and ultradurability. Here, we demonstrate that the generated interfacial CuAlO2 species can efficiently stabilize the highly active sites over the Cu-CuAlO2-Al2O3 catalyst under harsh electrochemical conditions without active sites regeneration for a long-term test. We show that this unique Cu-CuAlO2-Al2O3 catalyst exhibits ultradurable electrochemical CO2RR performance with an 85% C2 Faradaic efficiency for a 300 h test. Such a simple interfacial engineering design approach unveiled in this work would be adaptable to develop various ultradurable catalysts for industrial-scale electrochemical CO2RR.

Metallic Carbonitride MXene Based Photonic Hyperthermia for Tumor Therapy.

Photothermal therapy (PTT) as a noninvasive hyperthermia exhibits high potential for anti-cancer treatments. The explosion of efficient photothermal agents (PTAs) keeps developing rapidly. MXene stands out due to its intriguing structures, fantastic photodynamic properties, and good biocompatibility. However, the potential of MXenes has not been sufficiently explored in PTT. Its versatile chemical compositions of MXenes provide vast opportunities to discover new candidates. Considering that the metallic feature is mainly attributed to the metal element, anionic modulation may open a distinct avenue to propel efficient PTAs with metallic nature, which is expected for high light-harvesting over near-infrared (NIR)-I and NIR-II. As a paradigm, metal carbonitride is chosen to visualize the influences of anionic modulation. Taking advantage of electron injection from nitrogen, the distinct carbonitride Ti3 C1.15 N0.85 F0.88 O0.56 (OH)0.56 exhibits a strong NIR absorption (36.6 L g-1 cm-1 at 808 nm, 43.5 L g-1 cm-1 at 1064 nm), resulting in efficient photonic hyperthermia against tumors in vitro and in vivo. Looking through a large family of MXenes, this proof-of-principle demonstration offers a deep understanding between atomic composition and physicochemical properties, which further solidifies MXenes with all the potential for biomedical applications.

Highly Selective Photocatalytic CO2 Methanation with Water Vapor on Single-Atom Platinum-Decorated Defective Carbon Nitride.

Solar-driven CO2 methanation with water is an important route to simultaneously address carbon neutrality and produce fuels. It is challenging to achieve high selectivity in CO2 methanation due to competing reactions. Nonetheless, aspects of the catalyst design can be controlled with meaningful effects on the catalytic outcomes. We report highly selective CO2 methanation with water vapor using a photocatalyst that integrates polymeric carbon nitride (CN) with single Pt atoms. As revealed by experimental characterization and theoretical simulations, the widely explored Pt-CN catalyst is adapted for selective CO2 methanation with our rationally designed synthetic method. The synthesis creates defects in CN along with formation of hydroxyl groups proximal to the coordinated Pt atoms. The photocatalyst exhibits high activity and carbon selectivity (99 %) for CH4 production in photocatalytic CO2 reduction with pure water. This work provides atomic scale insight into the design of photocatalysts for selective CO2 methanation.

Pd-Modified ZnO-Au Enabling Alkoxy Intermediates Formation and Dehydrogenation for Photocatalytic Conversion of Methane to Ethylene.

Photocatalysis provides an intriguing approach for the conversion of methane to multicarbon (C2+) compounds under mild conditions; however, with methyl radicals as the sole reaction intermediate, the current C2+ products are dominated by ethane, with a negligible selectivity toward ethylene, which, as a key chemical feedstock, possesses higher added value than ethane. Herein, we report a direct photocatalytic methane-to-ethylene conversion pathway involving the formation and dehydrogenation of alkoxy (i.e., methoxy and ethoxy) intermediates over a Pd-modified ZnO-Au hybrid catalyst. On the basis of various in situ characterizations, it is revealed that the Pd-induced dehydrogenation capability of the catalyst holds the key to turning on the pathway. During the reaction, methane molecules are first dissociated into methoxy on the surface of ZnO under the assistance of Pd. Then these methoxy intermediates are further dehydrogenated and coupled with methyl radical into ethoxy, which can be subsequently converted into ethylene through dehydrogenation. As a result, the optimized ZnO-AuPd hybrid with atomically dispersed Pd sites in the Au lattice achieves a methane conversion of 536.0 µmol g-1 with a C2+ compound selectivity of 96.0% (39.7% C2H4 and 54.9% C2H6 in total produced C2+ compounds) after 8 h of light irradiation. This work provides fresh insight into the methane conversion pathway under mild conditions and highlights the significance of dehydrogenation for enhanced photocatalytic activity and unsaturated hydrocarbon product selectivity.

Ultrastable Cu Catalyst for CO2 Electroreduction to Multicarbon Liquid Fuels by Tuning C-C Coupling with CuTi Subsurface.

Production of multicarbon (C2+ ) liquid fuels is a challenging task for electrocatalytic CO2 reduction, mainly limited by the stabilization of reaction intermediates and their subsequent C-C couplings. In this work, we report a unique catalyst, the coordinatively unsaturated Cu sites on amorphous CuTi alloy (a-CuTi@Cu) toward electrocatalytic CO2 reduction to multicarbon (C2-4 ) liquid fuels. Remarkably, the electrocatalyst yields ethanol, acetone, and n-butanol as major products with a total C2-4 faradaic efficiency of about 49 % at -0.8 V vs. reversible hydrogen electrode (RHE), which can be maintained for at least 3 months. Theoretical simulations and in situ characterization reveals that subsurface Ti atoms can increase the electron density of surface Cu sites and enhance the adsorption of *CO intermediate, which in turn reduces the energy barriers required for *CO dimerization and trimerization.

Direct Observation of Dynamic Bond Evolution in Single-Atom Pt/C3 N4 Catalysts.

Single-atom catalysts are promising platforms for heterogeneous catalysis, especially for clean energy conversion, storage, and utilization. Although great efforts have been made to examine the bonding and oxidation state of single-atom catalysts before and/or after catalytic reactions, when information about dynamic evolution is not sufficient, the underlying mechanisms are often overlooked. Herein, we report the direct observation of the charge transfer and bond evolution of a single-atom Pt/C3 N4 catalyst in photocatalytic water splitting by synchronous illumination X-ray photoelectron spectroscopy. Specifically, under light excitation, we observed Pt-N bond cleavage to form a Pt0 species and the corresponding C=N bond reconstruction; these features could not be detected on the metallic platinum-decorated C3 N4 catalyst. As expected, H2 production activity (14.7 mmol h-1 g-1 ) was enhanced significantly with the single-atom Pt/C3 N4 catalyst as compared to metallic Pt-C3 N4 (0.74 mmol h-1 g-1 ).

Highly efficient, selective, and stable photocatalytic methane coupling to ethane enabled by lattice oxygen looping.

Light-driven oxidative coupling of methane (OCM) for multi-carbon (C2+) product evolution is a promising approach toward the sustainable production of value-added chemicals, yet remains challenging due to its low intrinsic activity. Here, we demonstrate the integration of bismuth oxide (BiOx) and gold (Au) on titanium dioxide (TiO2) substrate to achieve a high conversion rate, product selectivity, and catalytic durability toward photocatalytic OCM through rational catalytic site engineering. Mechanistic investigations reveal that the lattice oxygen in BiOx is effectively activated as the localized oxidant to promote methane dissociation, while Au governs the methyl transfer to avoid undesirable overoxidation and promote carbon─carbon coupling. The optimal Au/BiOx-TiO2 hybrid delivers a conversion rate of 20.8 millimoles per gram per hour with C2+ product selectivity high to 97% in the flow reactor. More specifically, the veritable participation of lattice oxygen during OCM is chemically looped by introduced dioxygen via the Mars-van Krevelen mechanism, endowing superior catalyst stability.

Spectroscopic visualization of reversible hydrogen spillover between palladium and metal-organic frameworks toward catalytic semihydrogenation.

Hydrogen spillover widely occurs in a variety of hydrogen-involved chemical and physical processes. Recently, metal-organic frameworks have been extensively explored for their integration with noble metals toward various hydrogen-related applications, however, the hydrogen spillover in metal/MOF composite structures remains largely elusive given the challenges of collecting direct evidence due to system complexity. Here we show an elaborate strategy of modular signal amplification to decouple the behavior of hydrogen spillover in each functional regime, enabling spectroscopic visualization for interfacial dynamic processes. Remarkably, we successfully depict a full picture for dynamic replenishment of surface hydrogen atoms under interfacial hydrogen spillover by quick-scanning extended X-ray absorption fine structure, in situ surface-enhanced Raman spectroscopy and ab initio molecular dynamics calculation. With interfacial hydrogen spillover, Pd/ZIF-8 catalyst shows unique alkyne semihydrogenation activity and selectivity for alkynes molecules. The methodology demonstrated in this study also provides a basis for further exploration of interfacial species migration.

Pushing the Performance Limit of Cu/CeO2 Catalyst in CO2 Electroreduction: A Cluster Model Study for Loading Single Atoms.

Pushing the performance limit of catalysts is a major goal of CO2 electroreduction toward practical application. A single-atom catalyst is recognized as a solution for achieving this goal, which is, however, a double-edged sword considering the limited loading amount and stability of single-atom sites. To overcome the limit, the loading of single atoms on supports should be well addressed, requiring a suitable model system. Herein, we report the model system of an ultrasmall CeO2 cluster (2.4 nm) with an atomic precise structure and a high surface-to-volume ratio for loading Cu single atoms. The combination of multiple characterizations and theoretical calculations reveals the loading location and limit of Cu single atoms on CeO2 clusters, determining an optimal configuration for CO2 electroreduction. The optimal catalyst achieves a maximum Faradaic efficiency (FE) of 67% and a maximum partial current density of -364 mA/cm2 for CH4, and can maintain high CH4 FE values over 50% in a wide range of applied current densities (-50 ∼ -600 mA/cm2), exceeding those of the reported catalysts.

Highly active, ultra-low loading single-atom iron catalysts for catalytic transfer hydrogenation.

Highly effective and selective noble metal-free catalysts attract significant attention. Here, a single-atom iron catalyst is fabricated by saturated adsorption of trace iron onto zeolitic imidazolate framework-8 (ZIF-8) followed by pyrolysis. Its performance toward catalytic transfer hydrogenation of furfural is comparable to state-of-the-art catalysts and up to four orders higher than other Fe catalysts. Isotopic labeling experiments demonstrate an intermolecular hydride transfer mechanism. First principles simulations, spectroscopic calculations and experiments, and kinetic correlations reveal that the synthesis creates pyrrolic Fe(II)-plN3 as the active center whose flexibility manifested by being pulled out of the plane, enabled by defects, is crucial for collocating the reagents and allowing the chemistry to proceed. The catalyst catalyzes chemoselectively several substrates and possesses a unique trait whereby the chemistry is hindered for more acidic substrates than the hydrogen donors. This work paves the way toward noble-metal free single-atom catalysts for important chemical reactions.

Sustainable methane utilization technology via photocatalytic halogenation with alkali halides.

Methyl halides are versatile platform molecules, which have been widely adopted as precursors for producing value-added chemicals and fuels. Despite their high importance, the green and economical synthesis of the methyl halides remains challenging. Here we demonstrate sustainable and efficient photocatalytic methane halogenation for methyl halide production over copper-doped titania using alkali halides as a widely available and noncorrosive halogenation agent. This approach affords a methyl halide production rate of up to 0.61 mmol h-1 m-2 for chloromethane or 1.08 mmol h-1 m-2 for bromomethane with a stability of 28 h, which are further proven transformable to methanol and pharmaceutical intermediates. Furthermore, we demonstrate that such a reaction can also operate solely using seawater and methane as resources, showing its high practicability as general technology for offshore methane exploitation. This work opens an avenue for the sustainable utilization of methane from various resources and toward designated applications.

Tuning the local electronic structure of a single-site Ni catalyst by co-doping a 3D graphene framework with B/N atoms toward enhanced CO2 electroreduction.

Various single metal sites supported on N-doped carbon materials have been demonstrated to be effective catalysts for CO2 electroreduction. However, it remains a challenging task to gain comprehensive understanding on how the local electronic structures of single metal catalytic sites are rationally tuned, which eventually holds the key to significantly enhance the electrocatalytic performance. Herein, we implement B-N bonds into an N-doped 3D graphene framework by B doping to further stabilize the supported catalytic Ni single-sites and simultaneously tune their local electronic structure. Moreover, electrochemical in situ Fourier-transform infrared spectroscopy reveals that the B-N bonds can further facilitate the production of pivotal *COOH intermediates in comparison with only N doping. As a result, the Ni single-site catalyst on the B, N co-doped 3D graphene framework achieves excellent catalytic performance with a CO faradaic efficiency (FE) of 98% and a turnover frequency (TOF) value of 20.1 s-1 at -0.8 V (vs. RHE), whereas the FE and TOF for the control sample without B doping are as low as 62% and 6.0 s-1, respectively. This work highlights the superiority of modulating local electronic structures of single-site catalysts toward efficient electrocatalytic CO2 reduction.

A Stacked Plasmonic Metamaterial with Strong Localized Electric Field Enables Highly Efficient Broadband Light-Driven CO2 Hydrogenation.

Light utilization largely governs the performance of CO2 photoconversion, whereas most of the materials that are implemented in such an application are restricted in a narrow spectral absorption range. Plasmonic metamaterials with a designable regular pattern and facile tunability are excellent candidates for maximizing light absorption to generate substantial hot electrons and thermal energy. Herein, a concept of coupling a Au-based stacked plasmonic metamaterial with single Cu atoms in alloy, as light absorber and catalytic sites, respectively, is reported for gas-phase light-driven catalytic CO2 hydrogenation. The metamaterial structure works in a broad spectral range (370-1040 nm) to generate high surface temperature for photothermal catalysis, and also induces strong localized electric field in favor of transfer of hot electrons and reduced energy barrier in CO2 hydrogenation. This work unravels the significant role of a strong localized electric field in photothermal catalysis and demonstrates a scalable fabrication approach to light-driven catalysts based on plasmonic metamaterials.

Atomically Dispersed Cu Sites on Dual-Mesoporous N-Doped Carbon for Efficient Ammonia Electrosynthesis from Nitrate.

The industrial Haber-Bosch process for ammonia synthesis is extremely important in modern society. However, it is energy intensive and leads to severe pollution, which has motivated eco-friendly NH3 synthesis research. Electroreduction of contaminant nitrate ions back to NH3 is an effective complement but is still limited by low NH3 yields and nitrate-to-NH3 selectivities. In this study, the electrochemical nitrate reduction reaction (NTRR) is carried out over a single-atom Cu catalyst. Atomically dispersed Cu sites anchored on dual-mesoporous N-doped carbon framework display excellent NTRR performance with NH3 production rate of 13.8 mol NH 3 gcat -1 h-1 and NO3 - -to-NH3 faradaic efficiency (FE) of 95.5 % at -1.0 V. Cu-N-C catalyst can sustain continuous 120 h NTRR test in the simulated NH3 synthesis scenarios with large current density (about 200 mA cm-2 ) and amplified volume of NO3 - solution (9 times). Theoretical calculations reveal that atomically dispersed Cu1 -N4 sites reduce the energy barrier of potential-determining step in NTRR and promote the decomposition of primary intermediate in NO3 - -to-N2 process. These findings provide a guideline for the rational design of highly active, selective and durable electrocatalysts for the NTRR.

Metal-Organic Frameworks Offering Tunable Binary Active Sites toward Highly Efficient Urea Oxidation Electrolysis.

Electrocatalytic urea oxidation reaction (UOR) is regarded as an effective yet challenging approach for the degradation of urea in wastewater into harmless N2 and CO2. To overcome the sluggish kinetics, catalytically active sites should be rationally designed to maneuver the multiple key steps of intermediate adsorption and desorption. Herein, we demonstrate that metal-organic frameworks (MOFs) can provide an ideal platform for tailoring binary active sites to facilitate the rate-determining steps, achieving remarkable electrocatalytic activity toward UOR. Specifically, the MOF (namely, NiMn0.14-BDC) based on Ni/Mn sites and terephthalic acid (BDC) ligands exhibits a low voltage of 1.317 V to deliver a current density of 10 mA cm-2. As a result, a high turnover frequency (TOF) of 0.15 s-1 is achieved at a voltage of 1.4 V, which enables a urea degradation rate of 81.87% in 0.33 M urea solution. The combination of experimental characterization with theoretical calculation reveals that the Ni and Mn sites play synergistic roles in maneuvering the evolution of urea molecules and key reaction intermediates during the UOR, while the binary Ni/Mn sites in MOF offer the tunability for electronic structure and d-band center impacting on the intermediate evolution. This work provides important insights into active site design by leveraging MOF platform and represents a solid step toward highly efficient UOR with MOF-based electrocatalysts.

Highly efficient overall urea electrolysis via single-atomically active centers on layered double hydroxide.

Anodic urea oxidation reaction (UOR) is an intriguing half reaction that can replace oxygen evolution reaction (OER) and work together with hydrogen evolution reaction (HER) toward simultaneous hydrogen fuel generation and urea-rich wastewater purification; however, it remains a challenge to achieve overall urea electrolysis with high efficiency. Herein, we report a multifunctional electrocatalyst termed as Rh/NiV-LDH, through integration of nickel-vanadium layered double hydroxide (LDH) with rhodium single-atom catalyst (SAC), to achieve this goal. The electrocatalyst delivers high HER mass activity of 0.262 A mg-1 and exceptionally high turnover frequency (TOF) of 2.125 s-1 at an overpotential of 100 mV. Moreover, exceptional activity toward urea oxidation is addressed, which requires a potential of 1.33 V to yield 10 mA cm-2, endorsing the potential to surmount the sluggish OER. The splendid catalytic activity is enabled by the synergy of the NiV-LDH support and the atomically dispersed Rh sites (located on the Ni-V hollow sites) as evidenced both experimentally and theoretically. The self-supported Rh/NiV-LDH catalyst serving as the anode and cathode for overall urea electrolysis (1 mol L-1 KOH with 0.33 mol L-1 urea as electrolyte) only requires a small voltage of 1.47 V to deliver 100 mA cm-2 with excellent stability. This work provides important insights into multifunctional SAC design from the perspective of support sites toward overall electrolysis applications.

Structural Reconstruction of Cu2 O Superparticles toward Electrocatalytic CO2 Reduction with High C2+ Products Selectivity.

Structural reconstruction is a process commonly observed for Cu-based catalysts in electrochemical CO2 reduction. The Cu-based precatalysts with structural complexity often undergo sophisticated structural reconstruction processes, which may offer opportunities for enhancing the electrosynthesis of multicarbon products (C2+ products) but remain largely uncertain due to various new structural features possibly arising during the processes. In this work, the Cu2 O superparticles with an assembly structure are demonstrated to undergo complicated structure evolution under electrochemical reduction condition, enabling highly selective CO2 -to-C2+ products conversion in electrocatalysis. As revealed by electron microscopic characterization together with in situ X-ray absorption spectroscopy and Raman spectroscopy, the building blocks inside the superparticle fuse to generate numerous grain boundaries while those in the outer shell detach to form nanogap structures that can efficiently confine OH- to induce high local pH. Such a combination of unique structural features with local reaction environment offers two important factors for facilitating C-C coupling. Consequently, the Cu2 O superparticle-derived catalyst achieves high faradaic efficiencies of 53.2% for C2 H4 and 74.2% for C2+ products, surpassing the performance of geometrically simpler Cu2 O cube-derived catalyst and most reported Cu electrocatalysts under comparable conditions. This work provides insights for rationally designing highly selective CO2 reduction electrocatalysts by controlling structural reconstruction.

High-performance photocatalytic nonoxidative conversion of methane to ethane and hydrogen by heteroatoms-engineered TiO2.

Nonoxidative coupling of methane (NOCM) is a highly important process to simultaneously produce multicarbons and hydrogen. Although oxide-based photocatalysis opens opportunities for NOCM at mild condition, it suffers from unsatisfying selectivity and durability, due to overoxidation of CH4 with lattice oxygen. Here, we propose a heteroatom engineering strategy for highly active, selective and durable photocatalytic NOCM. Demonstrated by commonly used TiO2 photocatalyst, construction of Pd-O4 in surface reduces contribution of O sites to valence band, overcoming the limitations. In contrast to state of the art, 94.3% selectivity is achieved for C2H6 production at 0.91 mmol g-1 h-1 along with stoichiometric H2 production, approaching the level of thermocatalysis at relatively mild condition. As a benchmark, apparent quantum efficiency reaches 3.05% at 350 nm. Further elemental doping can elevate durability over 24 h by stabilizing lattice oxygen. This work provides new insights for high-performance photocatalytic NOCM by atomic engineering.

Efficient photoelectrochemical CO2 conversion for selective acetic acid production.

Amidst the development of photoelectrochemical (PEC) CO2 conversion toward practical application, the production of high-value chemicals beyond C1 compounds under mild conditions is greatly desired yet challenging. Here, through rational PEC device design by combining Au-loaded and N-doped TiO2 plate nanoarray photoanode with Zn-doped Cu2O dark cathode, efficient conversion of CO2 to CH3COOH has been achieved with an outstanding Faradaic efficiency up to 58.1% (91.5% carbon selectivity) at 0.5 V vs. Ag/AgCl. Temperature programmed desorption and in situ Raman spectra reveal that the Zn-dopant in Cu2O plays multiple roles in selective catalytic CO2 conversion, including local electronic structure manipulation and active site modification, which together promote the formation of intermediate *CH2/*CH3 for C-C coupling. Apart from that, it is also unveiled that the sufficient electron density provided by the Au-loaded and N-doped TiO2 plate nanoarray photoanode plays an equally important role by initiating multi-electron CO2 reduction. This work provides fresh insights into the PEC system design to reach the multi-electron reduction reaction and facilitate the C-C coupling reaction toward high-value multicarbon (C2+) chemical production via CO2 conversion.