Si Doping-Induced Electronic Structure Regulation of Single-Atom Fe Sites for Boosted CO2 Electroreduction at Low Overpotentials.

Transition metal-based single-atom catalysts (TM-SACs) are promising alternatives to Au- and Ag-based electrocatalysts for CO production through CO2 reduction reaction. However, developing TM-SACs with high activity and selectivity at low overpotentials is challenging. Herein, a novel Fe-based SAC with Si doping (Fe-N-C-Si) was prepared, which shows a record-high electrocatalytic performance toward the CO2-to-CO conversion with exceptional current density (>350.0 mA cm-2) and ~100% Faradaic efficiency (FE) at the overpotential of <400 mV, far superior to the reported Fe-based SACs. Further assembling Fe-N-C-Si as the cathode in a rechargeable Zn-CO2 battery delivers an outstanding performance with a maximal power density of 2.44 mW cm-2 at an output voltage of 0.30 V, as well as high cycling stability and FE (>90%) for CO production. Experimental combined with theoretical analysis unraveled that the nearby Si dopants in the form of Si-C/N bonds modulate the electronic structure of the atomic Fe sites in Fe-N-C-Si to markedly accelerate the key pathway involving *CO intermediate desorption, inhibiting the poisoning of the Fe sites under high CO coverage and thus boosting the CO2RR performance. This work provides an efficient strategy to tune the adsorption/desorption behaviors of intermediates on single-atom sites to improve their electrocatalytic performance.

Sub-1 nm MoC Quantum Dots Decorating N-Doped Graphene as Advanced Electrocatalysts of Flexible Hybrid Alkali-Acid Zn-Quinone Battery.

The development of flexible energy devices is envisaged to revolutionize the next generation of the wearable electronics industry, the practical application yet faces critical issues of low power density, poor cycling stability, and low energy density. Herein, the authors report a newly flexible hybrid Zn-quinone battery (h-ZnQB) with acidic gel in the cathode and alkaline gel in the anode, in which proton (H+ ) and hydroxide ions (OH- ) are served as the ion charge carriers for acidic quinone cathode and alkaline Zn anode. To this end, the nanohybrids of sub-1 nm MoC quantum dots decorating nitrogen-doped ultrathin graphene (MoC QDs/NG) are developed as the advanced cathode electrocatalysts toward redox conversion between quinone and hydroquinone (H2 Q/Q). Comprehensive characterization studies and density functional theory (DFT) calculations reveal that high valent Mo species originating from the size-effects serve as the active sites for the conversion of H2 Q/Q, contributing to the impressive catalytic performance. The as-developed flexible h-ZnQB displays a high open-circuit voltage of 1.74 V with a specific capacity of 223.3 mAh g-1 and an energy density of 350 Wh kg-1 at 0.2 A g-1 , thanks to the fast kinetics of charge carriers (H+ and OH- ), the high activity of the catalyst, and the elaborate design of alkali-acid gel electrolytes.

Boosting Electroreduction Kinetics of Nitrogen to Ammonia via Tuning Electron Distribution of Single-Atomic Iron Sites.

Electrocatalytic nitrogen reduction reaction (NRR) plays a vital role for next-generation electrochemical energy conversion technologies. However, the NRR kinetics is still limited by the sluggish hydrogenation process on noble-metal-free electrocatalyst. Herein, we report the rational design and synthesis of a hybrid catalyst with atomic iron sites anchored on a N,O-doped porous carbon (FeSA -NO-C) matrix of an inverse opal structure, leading to a remarkably high NH3 yield rate of 31.9 µg NH 3 h-1 mg-1 cat. and Faradaic efficiency of 11.8 % at -0.4 V for NRR electrocatalysis, outperformed almost all previously reported atomically dispersed metal-nitrogen-carbon catalysts. Theoretical calculations revealed that the observed high NRR catalytic activity for the FeSA -NO-C catalyst stemmed mainly from the optimized charge-transfer between the adjacent O and Fe atoms homogenously distributed on the porous carbon support, which could not only significantly facilitate the transportation of N2 and ions but also effectively decrease the binding energy between the isolated Fe atom and *N2 intermediate and the thermodynamic Gibbs free energy of the rate-determining step (*N2 → *NNH).

Molten-Salt-Assisted Synthesis of Bismuth Nanosheets for Long-term Continuous Electrocatalytic Conversion of CO2 to Formate.

Two-dimensional (2D) monometallic pnictogens (antimony or Sb, and bismuth or Bi) nanosheets demonstrate potential in a variety of fields, including quantum devices, catalysis, biomedicine and energy, because of their unique physical, chemical, electronic and optical properties. However, the development of general and high-efficiency preparative routes toward high-quality pnictogen nanosheets is challenging. A general method involving a molten-salt-assisted aluminothermic reduction process is reported for the synthesis of Sb and Bi nanosheets in high yields (>90 %). Electrocatalytic CO2 reduction was investigated on the Bi nanosheets, and high catalytic selectively to formate was demonstrated with a considerable current density at a low overpotential and an impressive stability. Bi nanosheets continuously convert CO2 into formate in a flow cell operating for one month, with a yield rate of 787.5 mmol cm-2 h-1 . Theoretical results suggest that the edge sites of Bi are far more active than the terrace sites.

2 D Hybrid of Ni-LDH Chips on Carbon Nanosheets as Cathode of Zinc-Air Battery for Electrocatalytic Conversion of O2 into H2 O2.

It remains great challenge to develop precious-metal-free electrocatalysts to implement high-activity electrochemical conversion of O2 into value-added hydroperoxide species (HO2 - ), which are vulnerable when exposed to various transition-metal-based catalysts. A strategy based on steric hindrance and layered nickel-based layered double hydroxide (Ni-LDH) induction has been developed for one-pot inlaying high-density ultrathin 2 D Ni-LDH chips on in situ-grown carbon nanosheets (Ni-LDH C/CNSs). The resulting material exhibits high electrocatalytic selectivity with a faradaic efficiency up to 95 % for oxygen reduction into peroxide and attains a fairly high mass activity of approximately 22.2 A g-1 , outperforming most metal-based catalysts reported previously. Systematic studies demonstrate that the greatly increased defect concentration at Ni edge sites of Ni-LDH chips results in more active sites, which contributes a favorable thermodynamically neutral adsorption of OOH* and adsorbed H2 O2 molecules relatively weakly. Additionally, the modified CNSs effectively suppress H2 O2 decomposition and avoid O-O bond cleavage to produce H2 O by steric effects. The synergistic effect of CNSs and Ni-LDH chips therefore leads to high activity and high selectivity in a two-electron pathway. A proof-of-concept zinc-air fuel cell is proposed and set up to demonstrate the feasibility of green synthesis of peroxide, generating an impressive H2 O2 production rate of 5239.67 mmol h-1 gcat. -1 .

Interfacial engineering of Ru-S-Sb/antimonene electrocatalysts for highly efficient electrolytic hydrogen generation in neutral electrolyte.

The development of high-kinetic catalysts for the hydrogen evolution reaction (HER) in a neutral electrolyte is of great importance but unfortunately remains a challenge so far. Herein, we report hybrids with abundant Ru-S-Sb bonds and engineered ultrathin antimonene (Ru-S-Sb/antimonene) as highly kinetic, active, stable electrocatalysts for the HER in an aqueous neutral electrolyte. Experiments and density functional theory (DFT) calculations reveal that Ru-S-Sb bonds coupling with antimonene synergistically work to promote HER activity. The present study brings us one step closer to understand the structure-composition-property relationships and practical electrolytic H2 production.

A two-route CNN model for bank account classification with heterogeneous data.

Classifying bank accounts by using transaction data is encouraging in cracking down on illegal financial activities. However, few research simultaneously use heterogenous features, which are embedded in the time series data. In this paper, a two route convolution neural network TRHD-CNN model, fed with two types of heterogeneous feature matrices, is proposed for classifying the bank accounts. TRHD-CNN adopts divide and conquer strategy to extract characteristics from two types of data source independently. The strategy is proved able in mining complementary classification characteristics. We firstly transfer the original log data into a directed and dynamic transaction network. On the basis of that, two feature generation methods are devised for extracting information from local topological structure and time series transaction respectively. A DirectedWalk method is developed in this paper to learning the network vector of vertices used for embedding the neighbor relationship of bank account. The extensive experimental results, conducted on a real bank transaction dataset that contains illegal pyramid selling accounts, show the significant advantage of TRHD-CNN over the existing methods. TRHD-CNN can provide recall scores up to 5.15% higher than competing methods. In addition, the two-route architecture of TRHD-CNN is easy to extend to multi-route scenarios and other fields.

Oxygen-Containing Amorphous Cobalt Sulfide Porous Nanocubes as High-Activity Electrocatalysts for the Oxygen Evolution Reaction in an Alkaline/Neutral Medium.

A novel OER electrocatalyst, namely oxygen-incorporated amorphous cobalt sulfide porous nanocubes (A-CoS4.6 O0.6 PNCs), show advantages over the benchmark RuO2 catalyst in alkaline/neutral medium. Experiments combining with calculation demonstrate that the desirable O* adsorption energy, associated with the distorted CoS4.6 O0.6 octahedron structure and the oxygen doping, contribute synergistically to the outstanding electrocatalytic activity.

Oxyhydroxide Nanosheets with Highly Efficient Electron-Hole Pair Separation for Hydrogen Evolution.

The facile electron-hole pair recombination in earth-abundant transition-metal oxides is a major limitation for the development of highly efficient hydrogen evolution photocatalysts. In this work, the thickness of a layered ß-CoOOH semiconductor that contains metal/hydroxy groups was reduced to obtain an atomically thin, two-dimensional nanostructure. Analysis by ultrafast transient absorption spectroscopy revealed that electron-hole recombination is almost suppressed in the as-prepared 1.3 nm thick ß-CoOOH nanosheet, which leads to prominent electron-hole separation efficiencies of 60-90 % upon irradiation at 350-450 nm, which are ten times higher than those of the bulk counterpart. X-ray absorption spectroscopy and first-principles calculations demonstrate that [HO-CoO6-x] species on the nanosheet surface promote H(+) adsorption and H2 desorption. An aqueous suspension of the ß-CoOOH nanosheets exhibited a high hydrogen production rate of 160 µmol g(-1) h(-1) even when the system was operated for hundreds of hours.

CoOOH Nanosheets with High Mass Activity for Water Oxidation.

Endowing transition-metal oxide electrocatalysts with high water oxidation activity is greatly desired for production of clean and sustainable chemical fuels. Here, we present an atomically thin cobalt oxyhydroxide (γ-CoOOH) nanosheet as an efficient electrocatalyst for water oxidation. The 1.4 nm thick γ-CoOOH nanosheet electrocatalyst can effectively oxidize water with extraordinarily large mass activities of 66.6 A g(-1), 20 times higher than that of γ-CoOOH bulk and 2.4 times higher than that of the benchmarking IrO2 electrocatalyst. Experimental characterizations and first-principles calculations provide solid evidence to the half-metallic nature of the as-prepared nanosheets with local structure distortion of the surface CoO(6-x) octahedron. This greatly enhances the electrophilicity of H2O and facilitates the interfacial electron transfer between Co ions and adsorbed -OOH species to form O2, resulting in the high electrocatalytic activity of layered CoOOH for water oxidation.