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Electrochemical production of hydrogen peroxide (H2 O2 ) through two-electron (2 e- ) oxygen reduction reaction (ORR) is an on-site and clean route. Oxygen-doped carbon materials with high ORR activity and H2 O2 selectivity have been considered as the promising catalysts, however, there is still a lack of direct experimental evidence to identify true active sites at the complex carbon surface. Herein, we propose a chemical titration strategy to decipher the oxygen-doped carbon nanosheet (OCNS900 ) catalyst for 2 e- ORR. The OCNS900 exhibits outstanding 2 e- ORR performances with onset potential of 0.825 V (vs. RHE), mass activity of 14.5 A g-1 at 0.75 V (vs. RHE) and H2 O2 production rate of 770 mmol g-1 h-1 in flow cell, surpassing most reported carbon catalysts. Through selective chemical titration of C=O, C-OH, and COOH groups, we found that C=O species contributed to the most electrocatalytic activity and were the most active sites for 2 e- ORR, which were corroborated by theoretical calculations.

The alkaline electrocatalytic hydrogen evolution reaction (HER) is a potential way to realize industrial hydrogen production. However, the sluggish process of H2O dissociation, as well as the accumulation of OH− around the active sites, seriously limit the alkaline HER performance. In this work, we developed a unique CoS2 needle array grown on a carbon cloth (NAs@C) electrode as an alkaline HER catalyst. Finite-element simulations revealed that CoS2 needle arrays (NAs) induce stronger local electric field (LEF) than CoS2 disordered needles (DNs). This LEF can greatly repel the local OH− around the active sites, and then promote the forward H2O dissociation process. The local pH changes of the electrode surface confirmed the lower OH− concentration and stronger local pseudo-acidic environment of NAs@C compared to those of DNs@C. As a result, the NAs@C catalyst exhibited a low HER overpotential of 121 mV at a current density of 10 mA cm−2 in 1 M KOH, with the Tafel slope of 59.87 mV dec−1. This work provides a new insight into nanoneedle arrays for the alkaline HER by electric field-promoted H2O dissociation.

With the fast development of society and industry, atmospheric levels of carbon dioxide (CO2) have increased seriously, becoming a threat to the world’s climate. Electrochemical transformation of CO2 into fuels and chemicals using copper (Cu)-based materials has attracted enormous attention. However, the competitive hydrogen evolution reaction (HER) heavily influences their efficiency. Thus, it is urgent to promote the CO2 reduction reaction (CO2RR) and suppress the competitive HER. In this work, enhanced CO2RR with suppressed HER was achieved on polytetrafluoroethylene (PTFE) coated Cu nanoneedles (CuNNs). The concentration of surface adsorbed CO2 could be enhanced via the field-induced reagent concentration (FIRC) effect through the CuNN structures. The hydrophobic PTFE can prevent the supply of protons to CuNNs and thus suppress the HER. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS) revealed that the PTFE coated CuNNs maintained the nanoneedle structures and metallic Cu state during the catalytic reaction process. As a result, highly suppressed HER coupled with high C2 selectivity can be achieved on these PTFE coated CuNNs with a Faraday efficiency (FE) of 47% toward C2 products and an ultralow FE of 5.9% toward H2 at −1.49 V vs. RHE (without IR correction). This work provides an effective strategy to promote the CO2RR and suppress the competitive HER.

Ruthenium (Ru)-based catalysts, with considerable performance and desirable cost, are becoming highly interesting candidates to replace platinum (Pt) in the alkaline hydrogen evolution reaction (HER). The hydrogen binding at Ru sites (Ru-H) is an important factor limiting the HER activity. Herein, density functional theory (DFT) simulations show that the essence of Ru-H binding energy is the strong interaction between the 4 d z 2 orbital of Ru and the 1s orbital of H. The charge transfer between Ru sites and substrates (Co and Ni) causes the appropriate downward shift of the 4 d z 2 -band center of Ru, which results in a Gibbs free energy of 0.022 eV for H* in the RuCo system, much lower than the 0.133 eV in the pure Ru system. This theoretical prediction has been experimentally confirmed using RuCo alloy-nanosheets (RuCo ANSs). They were prepared via a fast co-precipitation method followed with a mild electrochemical reduction. Structure characterizations reveal that the Ru atoms are embedded into the Co substrate as isolated active sites with a planar symmetric and Z-direction asymmetric coordination structure, obtaining an optimal 4 d z 2 modulated electronic structure. Hydrogen sensor and temperature program desorption (TPD) tests demonstrate the enhanced Ru-H interactions in RuCo ANSs compared to those in pure Ru nanoparticles. As a result, the RuCo ANSs reach an ultra-low overpotential of 10 mV at 10 mA cm-2 and a Tafel slope of 20.6 mV dec-1 in 1 M KOH, outperforming that of the commercial Pt/C. This holistic work provides a new insight to promote alkaline HER by optimizing the metal-H binding energy of active sites.

Two-dimensional (2D) materials represented by graphene show numerous attractive electronic, optical, mechanical, and thermal properties. Especially, the extraordinary electronic and optical properties make 2D materials promising candidates for photodetectors to replace traditional ones that fails to meet the growing demands of many fields such as high frequency communication, national security, novel biomedical imaging and so on. However, several challenges must be overcome before the realization of commercially viable 2D materials-based photodetectors, such as the low photoresponsivity of intrinsic graphene due to its low optical absorption coefficient and zero bandgap induced high recombination ratio of photo-excited carrier, the poor carrier mobility of transition-metal-dichalcogenides (TMDCs), the instability and the difficulties in preparation of black phosphorus (BP) film. In the past few years, numerous efforts have been made persistently to improve the performance of the devices and several strategies were demonstrated to be effective. Here, we reviewed the latest advances of photodetectors which are based on typical 2D materials including graphene, TMDCs, BP, hexagonal boron-nitride (h-BN) as well as new layered-material (GaS, GaSe, InSe). We discuss the experimental challenges and describe the advances of different approaches by dividing them into four categories regarding the detection wavelength ranges including ultraviolet (UV), visible to near-infrared (Vis-NIR), mid- to far- infrared (MIR-FIR), and terahertz (THz).

The photoreduction of CO2 to hydrocarbon products has attracted much attention because it provides an avenue to directly synthesize value-added carbon-based fuels and feedstocks using solar energy. Among various photocatalysts, graphitic carbon nitride (g-C3N4) has emerged as an attractive metal-free visible-light photocatalyst due to its advantages of earth-abundance, nontoxicity, and stability. Unfortunately, its photocatalytic efficiency is seriously limited by charge carriers' ready recombination and their low reaction dynamics. Modifying the local electronic structure of g-C3N4 is predicted to be an efficient way to improve the charge transfer and reaction efficiency. Here, boron (B) is doped into the large cavity between adjacent tri-s-triazine units via coordination with two-coordinated N atoms. Theoretical calculations prove that the new electron excitation from N (2p x , 2p y ) to B (2p x , 2p y ) with the same orbital direction in B-doped g-C3N4 is much easier than N (2p x , 2p y ) to C 2p z in pure g-C3N4, and improves the charge transfer and localization, and thus the reaction dynamics. Moreover, B atoms doping changes the adsorption of CO (intermediate), and can act as active sites for CH4 production. As a result, the optimal sample of 1%B/g-C3N4 exhibits better selectivity for CH4 with ≈32 times higher yield than that of pure g-C3N4.

A steady sulfur cathode is central to realizing stable room temperature sodium-sulfur (RT Na-S) batteries. Here, sulfur atoms are incorporated into carbon to form thioether bond functionalized carbon (SC) as a cathode material for sodium storage, which is capable of the complete elimination or great suppression of the shuttle effect of soluble poly-sulfides by the generation of insoluble sulfides in RT Na-S batteries using an ordinary carbonate electrolyte. This thioether bond structure (C-S-C) in sulfur-doped carbon can be disassembled by the assistance of "voltage-scissors" in the low voltage range of 0.01-0.50 V vs. Na/Na+. The small sulfur species derived from the thioether bond structure react with the sodium anode to form insoluble sulfides. Moreover, the insoluble sulfides Na2S2 and Na2S are confined in the carbon defects induced by the cleaved sulfur to prevent them from degrading the long-chain poly-sulfides. The distinctive electrochemical performance of SC enriches our understanding of the sulfur cathode, and could provide novel insights for constructing stable sulfur cathode materials for specific energy storage devices.

Various yolk-shell structured particles designed for large volume expansion materials for lithium-ion storage have been reported, the cycle stability and coulombic efficiency can be effectively improved through such structure design. SnO2 has high theoretical capacity of 1494 mA h g−1 and 1378 mA h g−1 for lithium and sodium storage, respectively. The large volume expansion problem of SnO2 has long been considered as the primary reason for the capacity fading of SnO2 based anode materials. In this paper, the yolk-shell structured SnO2 porous nanowire has been designed, and this unique yolk-shell structure is reported as anode materials for lithium and sodium-ion storage for the first time. The yolk-shell structured porous nanowires deliver significantly improved cycle stability and coulombic efficiency as active material for both lithium and sodium-ion storage compared with that of pure SnO2 porous nanowires. It exhibits a high and stable capacity of 1150 mA h g−1 at current density of 200 mA g−1 for lithium-ion storage, and a capacity of 401 mA h g−1 at current density of 50 mA g−1 after 50 cycles for sodium-ion storage.

Coupling electrode composed of carbonaceous materials and metal oxides can effectively raise pseudocapacitance; however, due to the weak interaction between carbonaceous materials and metal oxides, structural control of the resultant coupling electrode remains a great challenge. Herein, surface-modified carbon cloth (SMCC), which is obtained by carbonizing the hydrothermal products of cetyltrimethylammonium bromide and glucose solution on carbon cloth (CC), is employed to regulate in-situ growth of δ-MnO2 in a KMnO4 and H2SO4 solution at hydrothermal condition. Structural characterizations indicate that surface modification renders SMCC to possess an oxygen-species-rich superhydrophilic surface, which in turn enables the supported δ-MnO2 to form the dense ultrathin nanosheets and abundant oxygen-vacancy (Vo) structure. Electrochemical tests demonstrate that the MnO2/SMCC can exhibit a specific capacitance of 508 F g−1 (792.5 C g−1) at 1 A g−1 under working potential range from −0.3 to 1.26 VAg/AgCl in three-electrode system, outperforming previously-reported δ-MnO2-based materials. Further, the detailed structural investigations identify that the oxygen species on SMCC dominate the generation of Vo in δ-MnO2 by reducing thickness and interface bonding, and the Vo in δ-MnO2 improves the pesudocapacitance by promoting the transition of Mn2+ to Mn4+.