Mg-Doped Cu Catalyst for Electroreduction of CO2 to Multicarbon Products: Lewis Acid Sites Simultaneously Promote *CO Adsorption and Water Dissociation.

The electroreduction of CO2 to valuable fuels or high-value chemicals by using sustainable electric energy provides a promising strategy for solving environmental problems dominated by the greenhouse effect. Copper-based materials are the only catalysts that can convert CO2 into multicarbon products, but they are plagued by high potential, low selectivity, and poor stability. The key factors to optimize the conversion of CO2 into multicarbon products are to improve the adsorption capacity of intermediates on the catalyst surface, accelerate the hydrogenation step, and improve the C-C coupling efficiency. Herein, we successfully doped Lewis acid Mg into Cu-based materials using a simple liquid-phase chemical method. In situ Raman and FT-IR tracking show that the Mg site enhances the surface coverage of the *CO intermediate, simultaneously promoting water dissociation. Under an industrial current density of 0.7 A cm-2, the FEC2+ reaches 73.9 ± 3.48% with remarkable stability. Density functional theory studies show that doping the Lewis acid Mg site increases the coverage of *CO and accelerates the splitting of water, thus promoting the C-C coupling efficiency, reducing the reaction energy barrier, and greatly improving the selectivity of C2+ products.

Enhancing local K+ adsorption by high-density cube corners for efficient electroreduction of CO2 to C2+ products.

Reducing carbon dioxide (CO2) to high value-added chemicals using renewable electricity is a promising approach to reducing CO2 levels in the air and mitigating the greenhouse effect, which depends on high-efficiency electrocatalysts. Copper-based catalysts can be used for electroreduction of CO2 to produce C2+ products with high added value, but suffer from poor stability and low selectivity. Herein, we propose a strategy to enhance the field effect by varying the cubic corner density on the surface of Cu2O microspheres for improving the electrocatalytic performance of CO2 reduction to C2+ products. Finite element method (FEM) simulation results show that the high density of cubic corners helps to enhance the local electric field, which increases the K+ concentration on the catalyst surface. The results of CO2 electroreduction tests show that the FEC2+ of the Cu2O catalyst with high-density cubic corners is 71% at a partial current density of 497 mA cm-2. Density functional theory (DFT) calculations reveal that Cu2O (111) and Cu2O (110) can effectively reduce the energy barrier of C-C coupling and improve the FEC2+ at high K+ concentrations relative to Cu2O (100). This study provides a new perspective for the design and development of efficient CO2RR catalysts.

Regulating the kinetics of zinc-ion migration in spinel ZnMn2O4 through iron doping boosted aqueous zinc-ion storage performance.

Spinel ZnMn2O4 with a three-dimensional channel structure is one of the important cathode materials for aqueous zinc ions batteries (AZIBs). However, like other manganese-based materials, spinel ZnMn2O4 also has problems such as poor conductivity, slow reaction kinetics and structural instability under long cycles. Herein, ZnMn2O4 mesoporous hollow microspheres with metal ion doping were prepared by a simple spray pyrolysis method and applied to the cathode of aqueous zinc ion battery. Cation doping not only introduces defects, changes the electronic structure of the material, improves its conductivity, structural stability, and reaction kinetics, but also weakens the dissolution of Mn2+. The optimized 0.1 % Fe-doped ZnMn2O4 (0.1% Fe-ZnMn2O4) has a capacity of 186.8 mAh g-1 after 250 charge-discharge cycles at 0.5 A g-1 and the discharge specific capacity reaches 121.5 mAh g-1 after 1200 long cycles at 1.0 A g-1. The theoretical calculation results show that doping causes the change of electronic state structure, accelerates the electron transfer rate, and improves the electrochemical performance and stability of the material.

InBi Bimetallic Sites for Efficient Electrochemical Reduction of CO2 to HCOOH.

Formic acid is receiving intensive attention as being one of the most progressive chemical fuels for the electrochemical reduction of carbon dioxide. However, the majority of catalysts suffer from low current density and Faraday efficiency. To this end, an efficient catalyst of In/Bi-750 with InOx nanodots load is prepared on a two-dimensional nanoflake Bi2 O2 CO3 substrate, which increases the adsorption of * CO2 due to the synergistic interaction between the bimetals and the exposure of sufficient active sites. In the H-type electrolytic cell, the formate Faraday efficiency (FE) reaches 97.17% at -1.0 V (vs reversible hydrogen electrode (RHE)) with no significant decay over 48 h. A formate Faraday efficiency of 90.83% is also obtained in the flow cell at a higher current density of 200 mA cm-2 . Both in-situ Fourier transform infrared spectroscopy (FT-IR) and theoretical calculations show that the BiIn bimetallic site can deliver superior binding energy to the * OCHO intermediate, thereby fundamentally accelerating the conversion of CO2 to HCOOH. Furthermore, assembled Zn-CO2 cell exhibits a maximum power of 6.97 mW cm-1 and a stability of 60 h.

Synergistic Acid Hydrogen Evolution of Neighboring Pt Single Atoms and Clusters: Understanding Their Superior Activity and Mechanism.

The hydrogen evolution reaction (HER) involves two-step elementary reactions, providing an opportunity to establish dual-site synergistic catalysts. This work demonstrates carbon-supported Pt single atoms and clusters (Pt1+Cs-NPC) as an efficient catalyst for acidic HER, which exhibits an ultralow Tafel slope of 12.5 mV/dec and an overpotential of 24 mV at 10 mA/cm2 with an ultralow platinum content of 3.8 wt %. The Pt mass activity and turnover frequency (TOF) are 10.2 times and 5.4 times that of commercial Pt/C, respectively. The density functional theory (DFT) study shows that the Pt cluster regulates the electronic state structure of the adjacent Pt single atom, so that the ΔGH* at the Pt1 site approaches 0. Moreover, the DFT study confirms that Pt clusters and neighboring Pt single atoms can synergistically catalyze the Tafel step and reduce the energy barrier in forming the H-H bond. At the same time, the platinum cluster reduces the energy barrier of the nearby platinum single-atom site to the Heyrovsky step and accelerates the reaction with hydrated hydrogen ions. Studies have shown that platinum clusters and platinum single-atom composite loading structures exhibit excellent activity for the Volmer-Tafel or Volmer-Heyrovsky reaction paths of HER reactions. This work provides a clear understanding of the synergistic effect of Pt1+Cs-NPC, which provides guidance for developing efficient HER catalysts.

MOF-derived multicomponent Fe2P-Co2P-Ni2P hollow architectures for efficient hydrogen evolution.

In this work, we introduce Fe and Ni into Co-MOF to construct a kind of multicomponent phosphide hollow architecture with walls assembled by nanosheets. The multicomponent nature can enhance the intrinsic catalytic activity, while the sheet-like surface and inter-sheet voids provide a large active area, which is beneficial for electrolyte penetration and gas generation. As expected, the optimized product has catalytic hydrogen evolution reaction (HER) overpotentials of 105 and 161 mV at current densities of 10 and 100 mA cm-2, respectively, and maintained long-term stability for over 100 hours at 10 mA cm-2 current densities.

High-Areal Density Single-Atoms/Metal Oxide Nanosheets: A Micro-Gas Blasting Synthesis and Superior Catalytic Properties.

The two-dimensional nanosheets are conducive to not only endow opened surfaces for loading active metal atoms but also boost the mass transfer for the heterogeneous reactions. The challenge is how to load and stabilize single-atoms on nanosheets in high-areal densities. This work reports an efficient micro-gas blasting (MGB) strategy to access versatile noble metal single-atoms/metal oxide nanosheets, including Ir1 /CoOx , Pd1 /CeO2 , etc. Especially for Pt/CeO2 nanosheets (Pt1 /CeO2 -S), the Pt loading is increased to 15 at%. The Pt1 /CeO2 -S catalysts from MGB are revealed to possess superior reactivity and tolerance in the model reaction of water-gas shift (WGS). The Pt1 /CeO2 -S catalyst exhibit 2-3 times reactivity that of their thicker counterpart, single-atom Pt1 /CeO2 microspheric catalyst. Moreover, the single-atom sites in Pt1 /CeO2 -S (1-10 %) catalysts are stable in a harsh WGS reaction condition of 10 % CO. This work thus paves a way to access the practical single-atom catalysts.

Structural engineering and electronic state tuning optimization of molybdenum-doped cobalt hydroxide nanosheet self-assembled hierarchical microtubules for efficient electrocatalytic oxygen evolution.

Cobalt-based hydroxide are ideal candidates for the oxygen evolution reaction. Herein, we use molybdenum oxide nanorods as sacrificial templates to construct a self-supporting molybdenum-doped cobalt hydroxide nanosheet hierarchical microtubule structure based on a structural engineering strategy to improve the active area of the catalyst. X-ray-based spectroscopic tests revealed that Mo (VI) with tetrahedral coordination intercalated into the interlayer of cobalt hydroxide, promoting interlayer separation. At the same time, Mo is connected with Co through oxygen bonds, which promotes the transfer of Co charges to Mo and reduces the electron cloud density of Co ions. In 1 M KOH, optimized molybdenum-doped cobalt hydroxide nanosheet microtubules only needs an overpotential of 288 mV to drive a current density of 10 mA cm-2, which is significantly better than that of pure Co(OH)2 nanosheets and RuO2. Structural engineering and electronic state regulation can effectively improve the oxygen evolution activity of cobalt-based hydroxide, which provides a design idea for the development of efficient oxygen evolution catalysts.

Scalable fabrication of NiCoMnO4 yolk-shell microspheres with gradient oxygen vacancies for high-performance aqueous zinc ion batteries.

Defect regulation, which enables better charge transfer and capacity retention in manganese-based cathode materials, is the key to the development of rechargeable aqueous zinc-ion batteries. Herein, yolk-shell structured NiCoMnO4-VO with gradient oxygen vacancies are synthesized by spray pyrolysis and ammonia etching. The generation of the yolk-shell structures are regulated by the diffusion rate of ions in the atomized droplets during the nucleation process instead of adding template agent. In addition, the etching effect of ammonia gradually dissolves nickel oxide in the material from the surface to the interior, creating abounding gradient oxygen vacancies and thereby achieving more active sites for zinc storage and faster charge transfer. Therefore, the material exhibits superior electrochemical performances with initial discharge capacities of 277.9 mA h g-1 at 0.2 A g-1, and the long-term capacities retention rate is 89.3% after 2800 cycles at 5 A g-1. Ex-situ XRD demonstrates NiCoMnO4-VO belongs to the embedding-extraction mechanism of H+ and Zn2+. In-situ optical microscopy reveals that the formation of zinc dendrites is suppressed to some extent.

Metal-Organic Framework-Derived BiIn Bimetallic Oxide Nanoparticles Embedded in Carbon Networks for Efficient Electrochemical Reduction of CO2 to Formate.

Bismuth-based catalysts exhibit excellent activity and selectivity for the electroreduction of carbon dioxide (CO2). However, single-component bismuth-based catalysts are not satisfactory for the electrochemical reduction of CO2 to formic acid, mainly due to their high hydrogen production, low electrical conductivity, and small catalytic current density. Herein, we used a coordination strategy to recombine Bi and In at the molecular level to form Bi/In bimetallic metal-organic frameworks (MOFs), which were then calcined to obtain MOF-derived Bi/In bimetallic oxide nanoparticles embedded in carbon networks. Thanks to the synergistic effect of bimetallic components, high specific surface area, suitable pore size distribution, and high electrical conductivity of the carbon network, the material exhibits excellent activity and selectivity for electroreduction of CO2 to formate. In H-type electrolyzers, the formate Faradaic efficiency reaches 91% at -0.9 V (vs RHE) and does not decrease significantly within 48 h. In situ Fourier transform infrared spectroscopy confirms the reaction intermediates and reveals that CO2 electroreduction is dominant by the *OCHO pathway.

Synergistic melamine intercalation and Zn(NO3)2 activation of N-doped porous carbon supported Fe/Fe3O4 for efficient electrocatalytic oxygen reduction.

Developing inexpensive, efficient and good stability transition metal-based oxygen reduction reaction (ORR) electrocatalysts is a research topic of great concern in the commercial application of fuel cells. Herein, with zinc nitrate as activator, iron nitrate as active component and melamine as intercalating agent and nitrogen source, an N-doped porous carbon supported Fe/Fe3O4 (Fe/Fe3O4@NC) catalyst is successfully synthesized by an impregnation-calcination method combined with freeze-drying technique. The positive onset potential (E onset), half-wave potential (E 1/2) and limiting current density (J L) of the optimal Fe/Fe3O4@NC catalyst are 1.012, 0.90 V vs. RHE and 5.87 mA cm-2, respectively. Furthermore, Fe/Fe3O4@NC catalyzes ORR mainly through a 4e- pathway, and the yield of H2O2 is less than 5%. It also manifests a robust stability after 5000 CV cycles of ADT testing, and the half-wave potential is only negatively shifted 17 mV. The structural characterization and experimental results further suggest that the outstanding ORR electrocatalytic performance of the Fe/Fe3O4@NC catalyst benefits from the synergetic effect of zinc nitrate activation and nitrogen doping, which can greatly improve the specific surface area, thus better dispersing more metal active sites. This work puts forward a simple and practicable way for preparing high-performance non-noble metal-based biomass ORR electrocatalysts.

Hexamethylenetetramine induced multidimensional defects in Co2P nanosheets for efficient alkaline hydrogen evolution.

Crystal engineering is an important way to improve the catalytic performance of transition-metal phosphides. In this work, we propose a strategy for constructing multi-dimensional defects induced by hexamethylenetetramine, which effectively introduces grain boundaries, N doping and P vacancies into Co2P nanosheets, and improves the activity and stability of the catalyst. Due to the synergistic effect of the multi-dimensional defects, the Co2P nanosheets exhibit excellent HER catalytic performance, especially at a large current density of 100 mA cm-2 with an overpotential of only 159 mV. Under 1 M KOH electrolyte and current density of 10 mA cm-2, the long-term test for 36 h shows that the catalyst maintains a very high stability.

Constructing an interspace in MnO@NC microspheres for superior lithium ion battery anodes.

In this work, silica nanospheres were introduced into nitrogen-carbon (NC) coated MnO microspheres and filled the gap between NC and MnO. After etching, an interspace was formed between the coating layer and the MnO microspheres. The structure not only provides a conductive NC layer, but also constructs a space to mitigate the volume effect of MnO. As expected, the specific capacity remained at 1143.93 mA h g-1 after 200 cycles at a current density of 0.2 A g-1, and 726.96 mA h g-1 after 450 cycles at a high current density of 1 A g-1. The superior performance can be attributed to the unique structure with an internal void space and the excellent protection of MnO microspheres by the surface NC layer.

Sandwich shelled TiO2@Co3O4@Co3O4/C hollow spheres as anode materials for lithium ion batteries.

A sandwich shelled hollow TiO2@Co3O4@Co3O4/C composite is synthesized by consecutive coating of Co3O4 nanosheets and TiO2 particles on Co3O4/C hollow spheres. The composite delivers an excellent lithium storage performance, maintaining 1081.78 mA h g-1 after 100 cycles at 0.2 A g-1 and 772.23 mA h g-1 after 300 cycles at 1 A g-1, due to its superior structure combining the advantages of each component with favorable electron-transfer, Li+-diffusion properties, and distinguished stability.

Freeze-drying assisted biotemplated route to 3D mesoporous Na3V2(PO4)3@NC composites as cathodes with high performance for sodium-ion batteries.

A facile freeze-drying assisted biotemplated route is developed to synthesize Na3V2(PO4)3 embedded in a N-doped three-dimensional mesoporous carbon framework, which has a superior initial discharge capacity and stability for Na-ion batteries.

A multi-interfacial FeOOH@NiCo2O4 heterojunction as a highly efficient bifunctional electrocatalyst for overall water splitting.

Electrocatalytic water decomposition is the key to sustainable energy, and the design and synthesis of cost-effective electrocatalysts is the main objective of electrocatalytic water splitting. In this paper, multi-interfacial FeOOH@NiCo2O4 hybrid nanoflowers are prepared through a two-step hydrothermal reaction. In such heterostructures, NiCo2O4 nanoflowers are coated with a layer of FeOOH nanoparticles. In addition, the obtained electrocatalyst could provide abundant electroactive sites and the formation of FeOOH@NiCo2O4 nanointerfaces can also improve the charge transfer rate. As a result, under the HER and OER conditions, the prepared catalysts show an outstanding electrocatalytic performance. Moreover, in a two-electrode water splitting system, the FeOOH@NiCo2O4 heterostructure, as a dual-function electrocatalyst, needs a cell voltage of only 1.58 V at a current density of 10 mA cm-2. This study provides a facile and feasible method to construct different kinds of heterostructures as bifunctional electrocatalysts with multiple interfaces by a simple hydrothermal method.

Titania supported synergistic palladium single atoms and nanoparticles for room temperature ketone and aldehydes hydrogenation.

Selective reduction of ketone/aldehydes to alcohols is of great importance in green chemistry and chemical engineering. Highly efficient catalysts are still demanded to work under mild conditions, especially at room temperature. Here we present a synergistic function of single-atom palladium (Pd1) and nanoparticles (PdNPs) on TiO2 for highly efficient ketone/aldehydes hydrogenation to alcohols at room temperature. Compared to simple but inferior Pd1/TiO2 and PdNPs/TiO2 catalysts, more than twice activity enhancement is achieved with the Pd1+NPs/TiO2 catalyst that integrates both Pd1 and Pd NPs on mesoporous TiO2 supports, obtained by a simple but large-scaled spray pyrolysis route. The synergistic function of Pd1 and PdNPs is assigned so that the partial Pd1 dispersion contributes enough sites for the activation of C=O group while PdNPs site boosts the dissociation of H2 molecules to H atoms. This work not only contributes a superior catalyst for ketone/aldehydes hydrogenation, but also deepens the knowledge on their hydrogenation mechanism and guides people to engineer the catalytic behaviors as needed.

Facile one-pot synthesis of novel hierarchical Bi2O3/Bi2S3 nanoflower photocatalyst with intrinsic p-n junction for efficient photocatalytic removals of RhB and Cr(VI).

The construction of heterojunction system can promote the separation and transfer of photogenerated electron-hole pairs, which is conducive to the degradation of sewage. In this paper, heterostructured Bi2O3/Bi2S3 nanoflowers are fabricated by a one-step hydrothermal method. The microstructure and optical absorption properties are studied through the detailed characterization of this heterojunction. The visible light photocatalytic ability of as-prepared Bi2O3/Bi2S3 heterojunctions are investigated by photocatalytic removals of RhB and Cr(VI). The results of photocatalysis indicate that removal efficiencies of RhB and Cr(VI) over Bi2O3/Bi2S3 heterojunction are higher than those of pure Bi2O3 and Bi2S3. The improved photocatalytic performance of the Bi2O3/Bi2S3 heterojunctions could be attributed to a combination of the p-n junction between the p-type Bi2S3 and n-type Bi2O3, and large specific surface areas (46.31 m2 g-1). Moreover, the probable photocatalytic mechanism of composite photocatalysts is explored in detail by active species trapping experiments, N2 adsorption-desorption, the transient photovoltage electrochemical impedance spectroscopy and photoluminescence measurements. This work provides new insights into building of the efficient and novel heterogeneous photocatalysts and other energy-related devices.

Dual-Mode Long-Lived Luminescence of Mn2+-Doped Nanoparticles for Multilevel Anticounterfeiting.

Luminescent nanoparticles with dual-mode long-lived luminescence are of great importance for their attractive applications in biosensing, bioimaging, and data encoding. Herein, we report the realization of up- and downconversion emission of Mn2+ dopants in multilayer nanoparticles of NaGdF4:Yb/Tm@NaGdF4:Ce/Mn@NaYF4 upon excitation at 980 and 254 nm, respectively. The dual-mode emission of the Mn2+ dopants at 531 nm have a long-lived lifetime up to ∼30 ms as a result of the spin-forbidden optical transition of Mn2+ within the 3d5 configuration. After ceasing steady excitation at the two wavelengths, the long-lived feature of Mn2+ luminescence allows a longer persistent time than lanthanide emissions, thereby enabling the ease of data decoding by a cell phone camera under a burst mode. The long-lived green upconversion emission also permits the generation of a long green tail emission upon dynamic excitation at 980 nm. These attributes make the as-prepared Mn2+-doped multilayer nanoparticles particularly attractive for multilevel anticounterfeiting.

Simultaneous and Reversible Triggering of the Phase Transfer and Luminescence Change of Amidine-Modified Carbon Dots by CO2.

The ability to reversibly manipulate the surface nature of luminescent nanoparticles upon external stimulation enables the development of advanced optical probes for biological sensing and data encoding. Herein, we report the synthesis of a new class of smart carbon dots (CDs) via surface modification of amine-enriched CDs with CO2-responsive groups of amidine. We present that alternative CO2 and N2 bubbling can not only lead to a reversible phase transfer of the CDs between an organic phase and an aqueous phase but also give rise to a corresponding reversible luminescence change between blue and cyan-green. We attribute these observations to changes in both the surface chemistry and the emission states of the CDs triggered by the alternative CO2/N2 introduction. We also find a similar luminescence change of the CDs upon alternative exposure to a humid vapor of CO2 and a mixture of NH3 and N2 at room temperature, allowing them to be used as a new class of optical materials for optical encoding.