Metal-Free Bifunctional Ordered Mesoporous Carbon for Reversible Zn-CO2 Batteries.

The fabrication of Zn-CO2 batteries is a promising technique for CO2 fixation and energy storage. Herein, nitrogen-doped ordered mesoporous carbon (NOMC) is adopted as a bifunctional metal-free electrocatalyst for CO2 reduction and oxygen evolution reaction in the near-neutral electrolyte. The ordered mesoporous structures and abundant N-dopings of NOMC facilitate the accessibility and utilization of the active sites, which endow NOMC with excellent electrocatalysis performance and outstanding stability. Especially, a nearly 100% CO Faradaic efficiency is achieved at an ultralow overpotential of 360 mV for CO2 reduction. When constructed as an aqueous rechargeable Zn-CO2 battery using NOMC as the cathode, it yields a high peak power density of 0.71 mW cm-2 , a good cyclability of 300 cycles, and excellent energy efficiency of 52.8% at 1.0 mA cm-2 .

Heteroatom coordination induces electric field polarization of single Pt sites to promote hydrogen evolution activity.

Herein, we reported a kind of single Pt site (Pt-SA) stabilized on an MXene support (Pt-SA/MXene) via the formation of Pt-O and Pt-Ti bonds to effectively catalyze the hydrogen evolution reaction (HER). Due to the local electric field polarization derived from its unique asymmetric coordination, Pt-SA/MXene displays remarkably higher catalytic HER activity in an alkaline electrolyte. In detail, the Pt-SA/MXene electrocatalyst only needs a low overpotential of 33 mV to reach a current density of 10 mA cm-2 and maintains the performance over 27 h. Besides, Pt-SA/MXene also has a competitive mass activity, 23.5 A mgPt-1, at an overpotential of 100 mV, which is 29.4 times greater than that of the commercial Pt/C counterpart. Density functional theory (DFT) calculations revealed that the polarized electric field could efficiently tailor the electronic structure of Pt-SA/MXene and reduce the energy barrier of adsorption/desorption of the H* intermediate step, further improving its HER catalytic activity.

Isolated copper single sites for high-performance electroreduction of carbon monoxide to multicarbon products.

Electrochemical carbon monoxide reduction is a promising strategy for the production of value-added multicarbon compounds, albeit yielding diverse products with low selectivities and Faradaic efficiencies. Here, copper single atoms anchored to Ti3C2Tx MXene nanosheets are firstly demonstrated as effective and robust catalysts for electrochemical carbon monoxide reduction, achieving an ultrahigh selectivity of 98% for the formation of multicarbon products. Particularly, it exhibits a high Faradaic efficiency of 71% towards ethylene at -0.7 V versus the reversible hydrogen electrode, superior to the previously reported copper-based catalysts. Besides, it shows a stable activity during the 68-h electrolysis. Theoretical simulations reveal that atomically dispersed Cu-O3 sites favor the C-C coupling of carbon monoxide molecules to generate the key *CO-CHO species, and then induce the decreased free energy barrier of the potential-determining step, thus accounting for the high activity and selectivity of copper single atoms for carbon monoxide reduction.

Modulating Single-Atom Palladium Sites with Copper for Enhanced Ambient Ammonia Electrosynthesis.

The electrochemical reduction of N2 to NH3 is emerging as a promising alternative for sustainable and distributed production of NH3 . However, the development has been impeded by difficulties in N2 adsorption, protonation of *NN, and inhibition of competing hydrogen evolution. To address the issues, we design a catalyst with diatomic Pd-Cu sites on N-doped carbon by modulation of single-atom Pd sites with Cu. The introduction of Cu not only shifts the partial density of states of Pd toward the Fermi level but also promotes the d-2π* coupling between Pd and adsorbed N2 , leading to enhanced chemisorption and activated protonation of N2 , and suppressed hydrogen evolution. As a result, the catalyst achieves a high Faradaic efficiency of 24.8±0.8 % and a desirable NH3 yield rate of 69.2±2.5 µg h-1 mgcat. -1 , far outperforming the individual single-atom Pd catalyst. This work paves a pathway of engineering single-atom-based electrocatalysts for enhanced ammonia electrosynthesis.

Engineering Atomic Sites via Adjacent Dual-Metal Sub-Nanoclusters for Efficient Oxygen Reduction Reaction and Zn-Air Battery.

N-coordinated transition-metal materials are crucial alternatives to design cost-effective, efficient, and highly durable catalysts for electrocatalytic oxygen reduction reaction. Herein, the synthesis of uniformly distributed Cu-Zn clusters on porous N-doped carbon, which are accompanied by Cu/Zn-Nx single sites, is demonstrated. X-ray absorption fine structure tests reveal the co-existence of M-N (M = Cu or Zn) and M-M bonds in the catalyst. The catalyst shows excellent oxygen reduction reaction (ORR) performance in an alkaline medium with a positive half-wave potential of 0.884 V, a superior kinetic current density of 36.42 mA cm-2 at 0.85 V, and a Tafel slope of 45 mV dec-1 , all of which are among the best-reported results. Furthermore, when employed as an air cathode in Zn-Air battery, it reveals a high open-cycle potential of 1.444 V and a peak power density of 164.3 mW cm-2 . Comprehensive experiments and theoretical calculations approved that the high activity of the catalyst can be attributed to the collaboration of the Cu/Zn-N4 sites with CuZn moieties on N-doped carbons.

Trifunctional Single-Atomic Ru Sites Enable Efficient Overall Water Splitting and Oxygen Reduction in Acidic Media.

Development of cost-effective, active trifunctional catalysts for acidic oxygen reduction (ORR) as well as hydrogen and oxygen evolution reactions (HER and OER, respectively) is highly desirable, albeit challenging. Herein, single-atomic Ru sites anchored onto Ti3 C2 Tx MXene nanosheets are first reported to serve as trifunctional electrocatalysts for simultaneously catalyzing acidic HER, OER, and ORR. A half-wave potential of 0.80 V for ORR and small overpotentials of 290 and 70 mV for OER and HER, respectively, at 10 mA cm-2 are achieved. Hence, a low cell voltage of 1.56 V is required for the acidic overall water splitting. The maximum power density of an H2 -O2 fuel cell using the as-prepared catalyst can reach as high as 941 mW cm-2 . Theoretical calculations reveal that isolated Ru-O2 sites can effectively optimize the adsorption of reactants/intermediates and lower the energy barriers for the potential-determining steps, thereby accelerating the HER, ORR, and OER kinetics.

Highly Productive Electrosynthesis of Ammonia by Admolecule-Targeting Single Ag Sites.

The ambient electrocatalytic N2 reduction reaction (NRR) is a promising alternative to the Haber-Bosch process for producing NH3. However, a guideless search for single-atom-based and other electrocatalysts cannot promote the NH3 yield rates by NRR efficiently. Herein, our first-principles calculations reveal that the successive emergence of vertical end-on *N2 and oblique end-on *NNH admolecules on single metal sites is key to high-performance NRR. By targeting the admolecules, single Ag sites with the Ag-N4 coordination are found and synthesized massively. They exhibit a record-high NH3 yield rate (270.9 µg h-1 mgcat.-1 or 69.4 mg h-1 mgAg-1) and a desirable Faradaic efficiency (21.9%) in HCl aqueous solution under ambient conditions. The generation rate of NH3 is stable during 20 consecutive reaction cycles, and the reduction current density is almost constant for 60 h. This work provides an effective targeting-design principle to purposefully synthesize active and durable single-atom-based NRR electrocatalysts.

Oxygen Doping Induced by Nitrogen Vacancies in Nb4 N5 Enables Highly Selective CO2 Reduction.

Surface vacancy engineering holds great promise for boosting the electrocatalytic activity for CO2 reduction reaction; however, the vacancies are generally unstable and may degrade into the inactive phase during electrolysis. Stabilizing the vacancy-enriched structure by heteroatoms can be an effective strategy to get a robust and active catalyst. Herein, a nitrogen-vacancy enriched Nb4 N5 on N-doped carbons is constructed, which is thereafter stabilized by a self-enhanced oxygen doping process. This oxygen-doped complex is used as an effective CO2 catalyst, which exhibits a maximum CO Faradaic efficiency of 91% at -0.8 V (vs reversible hydrogen electrode, RHE) and long-term stability throughout 30 h of electrocatalysis. Density function theory calculations suggest that the incorporation of oxygen in Nb4 N5 facilitates the formation of *COOH and thus promotes the CO2 reduction.

Boosting hydrogen evolution activity of vanadyl pyrophosphate nanosheets for electrocatalytic overall water splitting.

Herein, (VO)2P2O7 nanosheets function as a highly-active electrocatalyst for the hydrogen evolution reaction with an ultralow overpotential of 30 mV at 10 mA cm-2 in basic media, being close to Pt/C. Furthermore, as a bifunctional electrocatalyst, (VO)2P2O7 not only exhibits high activity but also good stability for overall water splitting.

AuCu Alloy Nanoparticle Embedded Cu Submicrocone Arrays for Selective Conversion of CO2 to Ethanol.

The CO2 reduction reaction (CO2 RR) driven by renewable electricity represents a promising strategy toward alleviating the energy shortage and environmental crisis facing humankind. Cu species, as one type of versatile electrocatalyst for the CO2 RR, attract tremendous research interest. However, for C2 products, ethanol formation is commonly less favored over Cu electrocatalysts. Herein, AuCu alloy nanoparticle embedded Cu submicrocone arrays (AuCu/Cu-SCA) are constructed as an active, selective, and robust electrocatalyst for the CO2 RR. Enhanced selectivity for EtOH is gained, whose Faradaic efficiency (FE) reaches 29 ± 4%, while ethylene formation is relatively inhibited (16 ± 4%) in KHCO3 aqueous solution. The ratio between partial current densities of EtOH and C2 H4 (jEtOH /jC2H4 ) can be tuned in the range from 0.15 ± 0.27 to 1.81 ± 0.55 by varying the Au content of the electrocatalysts. The combined experimental and theoretical calculation results identify the importance of Au in modifying binding energies of key intermediates, such as CH2 CHO*, CH3 CHO*, and CH3 CH2 O*, which consequently modify the activity and selectivity (jEtOH /jC2H4 ) for the CO2 RR. Moreover, AuCu/Cu-SCA also shows high durability with both the current density and FEEtOH being largely maintained for 24 h electrocatalysis.

Single-Atom Catalysts for the Electrocatalytic Reduction of Nitrogen to Ammonia under Ambient Conditions.

Powered by renewable electricity, the electrochemical reduction of nitrogen to ammonia is proposed as a promising alternative to the energy- and capital-intensive Haber-Bosch process, and has thus attracted much attention from the scientific community. However, this process suffers from low NH3 yields and Faradaic efficiency. The development of more effective electrocatalysts is of vital importance for the practical applications of this reaction. Of the reported catalysts, single-atom catalysts (SACs) show the significant advantages of efficient atom utilization and unsaturated coordination configurations, which offer great scope for optimizing their catalytic performance. Herein, progress in state-of-the-art SACs applied in the electrocatalytic N2 reduction reaction (NRR) is discussed, and the main advantages and challenges for developing more efficient electrocatalysts are also highlighted.

Unveiling the structural evolution of 1T SnS2 anode upon lithiation/delithiation by TEM.

Herein, the definite structure-dependent evolution process upon lithiation/delithiation and clear atomic images of pure 1T-phase SnS2 were obtained for the first time, illustrating the different insertion-conversion-desertion processes of discharge/charge plateaus. Also, 1T SnS2 exhibited advantages over commercial SnS2 (mixed with 1T and 1H phases) in cell resistance and lithium-storage performance.

Efficient Electroreduction CO2 to CO over MnO2 Nanosheets.

As a critical alternative step for the synthesis of important chemical feedstocks and complex carbon-based fuels, the electrochemical transformation of CO2 into CO holds great significance for the chemical industry. Here, MnO2 nanosheets array supported nickel foam has been synthesized and adopted as a binder-free catalyst for electrochemical CO2 reduction reaction (CO2RR). The well-distributed nanosheets of MnO2 impart a much higher density of accessible active sites for CO2RR, enabling the selective CO2 reduction to CO with a large current density (14.1 mA cm-2), excellent Faradaic efficiency (71%) and high electrochemical stability (10 h). This work first demonstrates the great potential of Mn-based oxides for electrocatalytic transformation of CO2 to valuable products.