Bipyridine-Confined Silver Single-Atom Catalysts Facilitate In-Plane C-O Coupling for Propylene Electrooxidation.

The electrooxidation of propylene presents a promising route for the production of 1,2-propylene glycol (PG) under ambient conditions. However, the C-O coupling process remains a challenge owing to the high energy barrier. In this work, we developed a highly efficient electrocatalyst of bipyridine-confined Ag single atoms on UiO-bpy substrates (Ag SAs/UiO-bpy), which exposed two in-plane coordination vacancies during reaction for the co-adsorption of key intermediates. Detailed structure and electronic property analyses demonstrate that CH3CHCH2OH* and *OH could stably co-adsorb in a square planar configuration, which then accelerates the charge transfer between them. The combination of stable co-adsorption and efficient charge transfer facilitates the C-O coupling process, thus significantly lowering its energy barrier. At 2.4 V versus a reversible hydrogen electrode, Ag SAs/UiO-bpy achieved a record-high activity of 61.9 gPG m-2 h-1. Our work not only presents a robust electrocatalyst but also advances a new perspective on catalyst design for propylene electrooxidation.

Atomic Defects Engineering Boosts Urea Synthesis toward Carbon Dioxide and Nitrate Coelectroreduction.

The atomic defect engineering could feasibly decorate the chemical behaviors of reaction intermediates to regulate catalytic performance. Herein, we created oxygen vacancies on the surface of In(OH)3 nanobelts for efficient urea electrosynthesis. When the oxygen vacancies were constructed on the surface of the In(OH)3 nanobelts, the faradaic efficiency for urea reached 80.1%, which is 2.9 times higher than that (20.7%) of the pristine In(OH)3 nanobelts. At -0.8 V versus reversible hydrogen electrode, In(OH)3 nanobelts with abundant oxygen vacancies exhibited partial current density for urea of -18.8 mA cm-2. Such a value represents the highest activity for urea electrosynthesis among recent reports. Density functional theory calculations suggested that the unsaturated In sites adjacent to oxygen defects helped to optimize the adsorbed configurations of key intermediates, promoting both the C-N coupling and the activation of the adsorbed CO2NH2 intermediate. In-situ spectroscopy measurements further validated the promotional effect of the oxygen vacancies on urea electrosynthesis.

Experimental Demonstration of Topological Catalysis for CO2 Electroreduction.

The past decade has witnessed substantial progress in understanding nontrivial band topology and discovering exotic topological materials in condensed-matter physics. Recently, topological physics has been further extended to the chemistry discipline, leading to the emergence of topological catalysis. In principle, the topological effect is detectable in catalytic reactions, but no conclusive evidence has been reported yet. Herein, by precisely manipulating the topological surface state (TSS) of Bi2Se3 nanosheets through thickness control and the application of a magnetic field, we provide direct experimental evidence to illustrate topological catalysis for CO2 electroreduction. With and without the cooperation of TSS, CO2 is mainly reduced into liquid fuels (HCOOH and H2C2O4) and CO, exhibiting high (up to 90% at -1.1 V versus reversible hydrogen electrode) and low Faradaic efficiency (FE), respectively. Theoretically, the product and FE difference can be attributed to the TSS-regulated adsorption of key intermediates and the reduced barrier of the potential-determining step. Our work demonstrates the inherent correlation between band topology and electrocatalysis, paving a new avenue for designing high-performance catalysts.

Probiotic nucleotides increase IL-10 expression in airway macrophages to mitigate airway allergy.

BACKGROUND: Dysfunctional immune regulation plays a crucial role in the pathogenesis of airway allergies. Macrophages are one of the components of the immune regulation cells. The aim of this study is to elucidate the role of lysine demethylase 5 A (KDM5A) in maintaining macrophages' immune regulatory ability. METHODS: DNA was extracted from Lactobacillus rhamnosus GG to be designated as LgDNA. LgDNA was administered to the mice through nasal instillations. M2 macrophages (M2 cells) were isolated from the airway tissues using flow cytometry. RESULTS: We found that airway M2 cells of mice with airway Th2 polarization had reduced amounts of IL-10 and KDM5A. Mice with Kdm5a deficiency in M2 cells showed the airway Th2 polarization. The expression of Kdm5a in airway M2 cells was enhanced by nasal instillations containing LgDNA. KDM5A mediated the effects of LgDNA on inducing the Il10 expression in airway M2 cells. Administration of LgDNA mitigated experimental airway allergy. CONCLUSIONS: M2 macrophages in the airway tissues of mice with airway allergy show low levels of KDM5A. By upregulating KDM5A expression, LgDNA can increase Il10 expression and reconcile airway Th2 polarization.

Fundamentals and Challenges of Ligand Modification in Heterogeneous Electrocatalysis.

The development of efficient catalytic materials in the energy field could promote the structural transformation from traditional fossil fuels to sustainable energy. In heterogeneous catalytic reactions, ligand modification is an effective way to regulate both electronic and steric structures of catalytic sites, thus paving a prospective avenue to design the interfacial structures of heterogeneous catalysts for energy conversion. Although great achievements have been obtained for the study and applications of heterogeneous ligand-modified catalysts, the systematical refinements of ligand modification strategies are still lacking. Here, we reviewed the ligand modification strategy from both the mechanistic and applicable scenarios by focusing on heterogeneous electrocatalysis. We elucidated the ligand-modified catalysts in detail from the perspectives of basic concepts, preparation, regulation of physicochemical properties of catalytic sites, and applications in different electrocatalysis. Notably, we bridged the electrocatalytic performance with the electronic/steric effects induced by ligand modification to gain intrinsic structure-performance relations. We also discussed the challenges and future perspectives of ligand modification strategies in heterogeneous catalysis.

Oriented Synthesis of Glycine from CO2, N2, and H2O via a Cascade Process.

Air contains carbon, hydrogen, oxygen, and nitrogen elements that are essential for the constitution of amino acids. Converting the air into amino acids, powered with renewable electricity, provides a green and sustainable alternative to petrochemical-based methods that produce waste and pollution. Here, taking glycine as an example, we demonstrated the complete production chain for electrorefining amino acids directly from CO2, N2, and H2O. Such a prospective Scheme was composed of three modules, linked by a spontaneous C-N bond formation process. The high-purity bridging intermediates, separated from the stepwise synthesis, boosted both the carbon selectivity from CO2 to glycine of 91.7 % and nitrogen selectivity from N2 to glycine of 98.7 %. Under the optimum condition, we obtained glycine with a partial current density of 160.8 mA cm-2. The high-purity solid glycine product was acquired with a separation efficiency of 98.4 %. This work unveils a green and sustainable method for the abiotic creation of amino acids from the air components.

Rational Design of Diatomic Active Sites for Elucidating Oxygen Evolution Reaction Performance Trends.

Diatomic catalysts, especially those with heteronuclear active sites, have recently attracted significant attention for their advantages over single-atom catalysts in reactions with relatively high energy barrier, e.g. oxygen evolution reaction. Rational design and synthesis of heteronuclear diatomic catalysts are of immense significance but have so far been plagued by the lack of a definitive correlation between structure and catalytic properties. Here, we report macrocyclic precursor constrained strategy to fabricate series of transition metal (MT, Ni, Co, Fe, Mn, or Cu)-noble (MN, Ir or Ru) centers in carbon material. One notable performance trend is observed in the order of Cu-MN

Dynamically Reversible Interconversion of Molecular Catalysts for Efficient Electrooxidation of Propylene into Propylene Glycol.

For the electrooxidation of propylene into 1,2-propylene glycol (PG), the process involves two key steps of the generation of *OH and the transfer of *OH to the C═C bond in propylene. The strong *OH binding energy (EB(*OH)) favors the dissociation of H2O into *OH, whereas the transfer of *OH to propylene will be impeded. The scaling relationship of the EB(*OH) plays a key role in affecting the catalytic performance toward propylene electrooxidation. Herein, we adopt an immobilized Ag pyrazole molecular catalyst (denoted as AgPz) as the electrocatalyst. The pyrrolic N-H in AgPz could undergo deprotonation to form pyrrolic N (denoted as AgPz-Hvac), which can be protonated reversibly. During propylene electrooxidation, the strong EB(*OH) on AgPz favors the dissociation of H2O into *OH. Subsequently, the AgPz transforms into AgPz-Hvac that possesses weak EB(*OH), benefiting to the further combination of *OH and propylene. The dynamically reversible interconversion between AgPz and AgPz-Hvac accompanied by changeable EB(*OH) breaks the scaling relationship, thus greatly lowering the reaction barrier. At 2.0 V versus Ag/AgCl electrode, AgPz achieves a remarkable yield rate of 288.9 mmolPG gcat-1 h-1, which is more than one order of magnitude higher than the highest value ever reported.

Dynamic Metal-Ligand Coordination Boosts CO2 Electroreduction.

The interfacial structure of heterogeneous catalysts determines the reaction rate by adjusting the adsorption behavior of reaction intermediates. Unfortunately, the catalytic performance of conventionally static active sites has always been limited by the adsorbate linear scaling relationship. Herein, we develop a triazole-modified Ag crystal (Ag crystal-triazole) with dynamic and reversible interfacial structures to break such a relationship for boosting the catalytic activity of CO2 electroreduction into CO. On the basis of surface science measurements and theoretical calculations, we demonstrated the dynamic transformation between adsorbed triazole and adsorbed triazolyl on the Ag(111) facet induced by metal-ligand conjugation. During CO2 electroreduction, Ag crystal-triazole with the dynamically reversible transformation of ligands exhibited a faradic efficiency for CO of 98% with a partial current density for CO as high as -802.5 mA cm-2. The dynamic metal-ligand coordination not only reduced the activation barriers of CO2 protonation but also switched the rate-determining step from CO2 protonation to the breakage of C-OH in the adsorbed COOH intermediate. This work provided an atomic-level insight into the interfacial engineering of the heterogeneous catalysts toward highly efficient CO2 electroreduction.

Enhancing CO2 Electroreduction Selectivity toward Multicarbon Products via Tuning the Local H2O/CO2 Molar Ratio.

Mass transfer plays an important role in controlling the surface coverage of reactants and the kinetics of surface reactions, thus significantly adjusting the catalytic performance. Herein, we reported that H2O diffusion was modulated by controlling the thicknesses of the carbon black (CB) layer between the gas diffusion electrode (GDE) of Cu and the electrolyte. As a consequence, the product distribution over the GDE of Cu was effectively regulated during CO2 electroreduction. Interestingly, a volcano-type relationship between the thickness of the CB layer and the faradaic efficiency (FE) for multicarbon (C2+) products was observed over the GDE of Cu. Especially, when the applied total current density was set as 800 mA cm-2, the FE for the C2+ products over the GDE of Cu coated by a CB layer with a thickness of 6.6 µm reached 63.2%, which was 2.8 times higher than that (16.8%) over the GDE of Cu without a CB layer.

Understanding the Effect of *CO Coverage on C-C Coupling toward CO2 Electroreduction.

Cu-based tandem nanocrystals have been widely applied to produce multicarbon (C2+) products via enhancing CO intermediate (*CO) coverage toward CO2 electroreduction. Nevertheless, it remains ambiguous to understand the intrinsic correlation between *CO coverage and C-C coupling. Herein, we constructed a tandem catalyst via coupling CoPc with the gas diffusion electrode of Cu (GDE of Cu-CoPc). A faradaic efficiency for C2+ products of 82% was achieved over a GDE of Cu-CoPc at an applied current density of 480 mA cm-2 toward CO2 electroreduction, which was 1.8 times as high as that over the GDE of Cu. Based on in situ experiments and density functional theory calculations, we revealed that the high *CO coverage induced by CO-generating CoPc promoted the local enrichment of *CO with the top adsorption mode, thus reducing the energy barrier for the formation of OCCO intermediate. This work provides an in-depth understanding of the surface coverage-dependent mode-specific C-C coupling mechanism toward CO2 electroreduction.

Adjusting Local CO Confinement in Porous-Shell Ag@Cu Catalysts for Enhancing C-C Coupling toward CO2 Eletroreduction.

Tuning the local confinement of reaction intermediates is of pivotal significance to promote C-C coupling for enhancing the selectivity for multicarbon (C2+) products toward CO2 electroreduction. Herein, we have gained insights into the confinement effect of local CO concentration for enhanced C-C coupling over core-shell Ag@Cu catalysts by tuning the pore diameters within porous Cu shells. During CO2 electroreduction, the core-shell Ag@Cu catalysts with an average pore diameter of 4.9 nm within the Cu shells (Ag@Cu-p4.9) exhibited the highest Faradaic efficiency of 73.7% for C2+ products at 300 mA cm-2 among the three Ag@Cu catalysts. Finite-element-method simulations revealed that the pores with a diameter of 4.9 nm in Cu conspicuously enhanced the local CO concentration. On the basis of in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy measurements, Ag@Cu-p4.9 exhibited the highest surface coverage of adsorbed CO intermediates with a linear adsorption configuration due to the confinement effect, thus facilitating C-C coupling.

Tuning the Electronic and Steric Interaction at the Atomic Interface for Enhanced Oxygen Evolution.

The two-dimensional surface or one-dimensional interface of heterogeneous catalysts is essential to determine the adsorption strengths and configurations of the reaction intermediates for desired activities. Recently, the development of single-atom catalysts has enabled an atomic-level understanding of catalytic processes. However, it remains obscure whether the conventional concept and mechanism of one-dimensional interface are applicable to zero-dimensional single atoms. In this work, we arranged the locations of single atoms to explore their interfacial interactions for improved oxygen evolution. When iridium single atoms were confined into the lattice of CoOOH, efficient electron transfer between Ir and Co tuned the adsorption strength of oxygenated intermediates. In contrast, atomic iridium species anchored on the surface of CoOOH induced inappreciable modification in electronic structures, whereas steric interactions with key intermediates at its Ir-OH-Co interface played a primary role in reducing its energy barrier toward oxygen evolution.

Doping regulation in transition metal compounds for electrocatalysis.

In electrocatalysis, doping regulation has been considered as an effective method to modulate the active sites of catalysts, providing a powerful means for creating a large variety of highly efficient catalysts for various reactions. Of particular interest, there has been growing research concerning the doping of two-dimensional transition-metal compounds (TMCs) to optimize their electrocatalytic performance. Despite the previous achievements, mechanistic insights of doping regulation in TMCs for electrocatalysis are still lacking. Herein, we provide a systematic overview of doping regulation in TMCs in terms of background, preparation, impacts on physicochemical properties, and typical applications including the hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, CO2 reduction reaction, and N2 reduction reaction. Notably, we bridge the understanding between the doping regulation of catalysts and their catalytic activities via focusing on the physicochemical properties of catalysts from the aspects of vacancy concentrations, phase transformation, surface wettability, electrical conductivity, electronic band structure, local charge distribution, tunable adsorption strength, and multiple adsorption configurations. We also discuss the existing challenges and future perspectives in this promising field.

Electronic Tuning of SnS2 Nanosheets by Hydrogen Incorporation for Efficient CO2 Electroreduction.

Surface functionalization with atoms serves as an important strategy to modulate the catalytic activities of low-dimensional nanomaterials. Herein, we developed a facile hydrogen incorporation strategy for improving the catalytic activities of SnS2 nanosheets toward CO2 electroreduction. Compared with SnS2 nanosheets, the hydrogen-incorporated SnS2 (denoted as H-SnS2) nanosheets exhibited high current density and Faradaic efficiency (FE) for formate. At -0.9 V vs RHE, H-SnS2 nanosheets displayed a maximum FE of 93% for carbonaceous product, which rivals the activities of most Sn-based catalysts in CO2 electroreduction. Mechanistic studies disclosed that the incorporation of surface hydrogen induced the electron injection into the structures of H-SnS2 nanosheets, which largely facilitates the process of CO2 activation. Density functional theory (DFT) calculations further revealed that hydrogen incorporation decreased the energy barrier for the formation of HCOO* intermediates, thus contributing to the CO2-to-formate conversion on H-SnS2 nanosheets.

Bias-Adaptable CO2-to-CO Conversion via Tuning the Binding of Competing Intermediates.

CO2 electroreduction powered by renewable electricity represents a promising method to enclose anthropogenic carbon cycle. Current catalysts display high selectivity toward the desired product only over a narrow potential window due primarily to unoptimized intermediate binding. Here, we report a functional ligand modification strategy in which palladium nanoparticles are encapsulated inside metal-organic frameworks with 2,2'-bipyridine organic linkers to tune intermediate binding and thus to sustain a highly selective CO2-to-CO conversion over widened potential window. The catalyst exhibits CO faradaic efficiency in excess of 80% over a potential window from -0.3 to -1.2 V and reaches the maxima of 98.2% at -0.8 V. Mechanistic studies show that the 2,2'-bipyridine on Pd surface reduces the binding strength of both *H and *CO, a too strong binding of which leads to competing formate production and CO poison, respectively, and thus enhances the selectivity and stability of CO product.

In-Situ Surface Reconstruction of InN Nanosheets for Efficient CO2 Electroreduction into Formate.

Probing and understanding the intrinsic active sites of electrocatalysts is crucial to unravel the underlying mechanism of CO2 electroreduction and provide a prospective for the rational design of high-performance electrocatalysts. However, their structure-activity relationships are not straightforward because electrocatalysts might reconstruct under realistic working conditions. Herein, we employ in-situ measurements to unveil the intrinsic origin of the InN nanosheets which served as an efficient electrocatalyst for CO2 reduction with a high faradaic efficiency of 95% for carbonaceous product. During the CO2 electroreduction, InN nanosheets reconstructed to form the In-rich surface. Density functional theory calculations revealed that the reconstruction of InN led to the redistribution of surface charge that significantly promoted the adsorption of HCOO* intermediates and thus benefited the formation of formate toward CO2 electroreduction. This work establishes a fundamental understanding on the mechanism associated with self-reconstruction of heterogeneous catalysts toward CO2 electroreduction.

Atomic-Level Construction of Tensile-Strained PdFe Alloy Surface toward Highly Efficient Oxygen Reduction Electrocatalysis.

Exploring the high-performance non-Pt electrocatalysts for oxygen reduction reaction (ORR), the bottleneck process in fuel cells, is desirable but challenging. Here, we report the Pd@PdFe core-shell icosahedra as an active and durable electrocatalyst toward ORR in alkaline conditions, which feature a three-atomic-layer tensile-strained PdFe overlayer on Pd icosahedra. Our optimized catalyst shows 2.8-fold enhancement in mass activity and 6.9-fold enhancement in specific activity than commercial Pt/C catalyst toward ORR, representing one of the best non-Pt electrocatalysts. Moreover, the boosted ORR catalysis is strongly supported by the assembled fuel cell performance using Pd@PdFe core-shell icosahedra as the cathode electrocatalyst. The density functional theory calculations reveal that the synergistic coupling of tensile strain and alloy effects enables the optimum binding strength for intermediates, thus causing the maximum activity. The present work suggests the coupling between multiple surface modulations endows larger room for the rational design of remarkable catalysts.

Molecular Modification of Single Cobalt Sites Boosts the Catalytic Activity of CO2 Electroreduction into CO.

Electroreduction of CO2 into carbonaceous fuels or industrial chemicals using renewable energy sources is an ideal way to promote global carbon recycling. Thus, it is of great importance to develop highly selective, efficient, and stable catalysts. Herein, we prepared cobalt single atoms (Co SAs) coordinated with phthalocyanine (Co SAs-Pc). The anchoring of phthalocyanine with Co sites enabled electron transfer from Co sites to CO2 effectively via the π-conjugated system, resulting in high catalytic performance of CO2 electroreduction into CO. During the process of CO2 electroreduction, the Faradaic efficiency (FE) of Co SAs-Pc for CO was as high as 94.8 %. Meanwhile, the partial current density of Co SAs-Pc for CO was -11.3 mA cm-2 at -0.8 V versus the reversible hydrogen electrode (vs RHE), 18.83 and 2.86 times greater than those of Co SAs (-0.60 mA cm-2 ) and commercial Co phthalocyanine (-3.95 mA cm-2 ), respectively. In an H-cell system operating at -0.8 V vs RHE over 10 h, the current density and FE for CO of Co SAs-Pc dropped by 3.2 % and 2.5 %. A mechanistic study revealed that the promoted catalytic performance of Co SAs-Pc could be attributed to the accelerated reaction kinetics and facilitated CO2 activation.

Single Atoms of Iron on MoS2 Nanosheets for N2 Electroreduction into Ammonia.

Efforts have been devoted to achieving a highly efficient artificial synthesis of ammonia (NH3 ). Reported herein is a novel Fe-MoS2 catalyst with Fe atomically dispersed onto MoS2 nanosheets, imitating natural nitrogenase, to boost N2 electroreduction into NH3 at room temperature. The Fe-MoS2 nanosheets exhibited a faradic efficiency of 18.8 % with a yield rate of 8.63 µg NH 3 mgcat. -1 h-1 for NH3 at -0.3 V versus the reversible hydrogen electrode. The mechanism study revealed that the electroreduction of N2 was promoted and the competing hydrogen evolution reaction was suppressed by decorating the edge sites of S in MoS2 with the atomically dispersed Fe, resulting in high catalytic performance for the electroreduction of N2 into NH3 . This work provides new ideas for the design of catalysts for N2 electroreduction and strengthens the understanding about N2 activation over Mo-based catalysts.