Electrochemical CO2 reduction is a key technology to recycle CO2 as a renewable resource, but adsorbing CO2 on the catalyst surface is challenging. We explored the effects of reduced graphene oxide (rGO) in Sn/rGO composites and found that the CO2 adsorption ability of Sn/rGO was almost 4-times higher than that of bare Sn catalysts. Density functional theory calculations revealed that the oxidized functional groups of rGO offered adsorption sites for CO2 toward the adjacent Sn surface and that CO2-rich conditions near the surface facilitated the production of formate via COOH* formation while suppressing CO* formation. Scanning electrochemical cell microscopy directly indicated that CO2 reduction was accelerated at the interface, together with the kinetic suppression of undesirable and competitive hydrogen evolution at the interface. Thus, the synergism of Sn/rGO ensures a substantial/rapid supply of CO2 from the functional groups to the Sn surface, thereby enhancing the Faradaic efficiency 1.8-times compared with that obtained with bare Sn catalysts.

Carbon‐based metal‐free catalysts for the hydrogen evolution reaction (HER) are essential for the development of a sustainable hydrogen society. Identification of the active sites in heterogeneous catalysis is key for the rational design of low‐cost and efficient catalysts. Here, by fabricating holey graphene with chemically dopants, the atomic‐level mechanism for accelerating HER by chemical dopants is unveiled, through elemental mapping with atomistic characterizations, scanning electrochemical cell microscopy (SECCM), and density functional theory (DFT) calculations. It is found that the synergetic effects of two important factors—edge structure of graphene and nitrogen/phosphorous codoping—enhance HER activity. SECCM evidences that graphene edges with chemical dopants are electrochemically very active. Indeed, DFT calculation suggests that the pyridinic nitrogen atom could be the catalytically active sites. The HER activity is enhanced due to phosphorus dopants, because phosphorus dopants promote the charge accumulations on the catalytically active nitrogen atoms. These findings pave a path for engineering the edge structure of graphene in graphene‐based catalysts.

Identifying the influence of the phase of a catalyst on its reactivity is crucial for guiding the rational design of highly active electrocatalysts. Herein, we unveil the phasedependent reactivity of nickel molybdates (NiMoO 4 ) for the electrocatalytic urea oxidation reaction (UOR). Various NiMoO 4 phases, namely, α-NiMoO 4 , β-NiMoO 4 , and the hydrate NiMoO 4 •xH 2 O, were synthesized, and their structural characteristics and electrochemical properties were related to their electrocatalytic performance for the UOR. The NiMoO 4 phase was found to determine its reactivity, and phase-dependent UOR activities were observed. In particular, β-NiMoO 4 exhibited a higher activity and faster kinetics than NiMoO 4 •xH 2 O and α-NiMoO 4 , which was attributed to the large electrochemical surface area, low Tafel slope, and small charge− transfer resistance of β-NiMoO 4 . Moreover, hydrogen generation via β-NiMoO 4 -catalyzed urea electrolysis achieved a much lower cell voltage (1.498 V to reach 10 mA cm −2 ) than that required for water electrolysis (1.633 V to reach 10 mA cm −2 ). This work provides insights into design strategies for high-activity electrocatalysts for energy-efficient hydrogen production.

carrier, in addition to the application of fuel cells operating on hydrogen-rich fuel. Water electrolysis driven by renewable energy is a promising technology [1][2][3] for hydrogen production with zero emission. Water electrolysis can be classified into the following types: alkaline, [4] proton exchange membrane (PEM), [5,6] and anion exchange membrane (AEM). [7,8] Compared to the other types, PEM-type water electrolysis is considered to be more ecofriendly and efficient because it generates no waste, produces highly pure H 2 gas (>99.9999 vol%), [9] and displays a high discharge H 2 pressure (3.0-7.6 MPa) [10] and a high current density (1.0-4.0 A cm −2 ) at low overpotentials (1.5-1.9 V). [3,6,10,11] In contrast, alkaline-and AEM-type water electrolysis produces H 2 with >99.5 vol% and >99.99 vol% purities, respectively. However, efficient electrocatalytic reactions in these systems require considerable amounts of noble metals, for example, 300 kg of Pt in the cathode and 700 kg of Ir in the anode per 1.0 GW of power input of the PEM-type electrolyzer. [11] The serious scarcity of noble metals, especially that of Ir (global production: ≈7 ton year −1 ), [11] To realize a sustainable hydrogen economy, corrosion-resistant non-noblemetal catalysts are needed to replace noble-metal-based catalysts. The combination of passivation elements and catalytically active elements is crucial for simultaneously achieving high corrosion resistance and high catalytic activity. Herein, the self-selection/reconstruction characteristics of multielement (nonary) alloys that can automatically redistribute suitable elements and rearrange surface structures under the target reaction conditions during the oxygen evolution reaction are investigated. The following synergetic effect (i.e., cocktail effect), among the elements Ti, Zr, Nb, and Mo, significantly contributes to passivation, whereas Cr, Co, Ni, Mn, and Fe enhance the catalytic activity. According to the practical water electrolysis experiments, the self-selected/reconstructed multi-element alloy demonstrates high performance under a similar condition with proton exchange membrane (PEM)-type water electrolysis without obvious degradation during stability tests. This verifies the resistance of the alloy to corrosion when used as an electrode under a practical PEM electrolysis condition.

Bottom-up synthesis of porous NiMo alloy reduced by NiMoO 4 nanofibers was systematically investigated to fabricate non-noble metal porous electrodes for hydrogen production. The different annealing temperatures of NiMoO 4 nanofibers under hydrogen atmosphere reveal that the 950 • C annealing temperature is key for producing bicontinuous porous NiMo alloy without oxide phases. The porous NiMo alloy acts as a cathode in electrical water splitting, which demonstrates not only almost identical catalytic activity with commercial Pt/C in 1.0 M KOH solution, but also superb stability for 12 days at an electrode potential of −200 mV vs. reversible hydrogen electrode (RHE).

Electrochemical water splitting is an ecofriendly technology for generating oxygen and hydrogen from water. The electrode is a key component that controls the efficiency of water splitting. Although noble metals such as Pt, Ru and Ir can achieve high energy efficiencies, their application in water splitting is limited by their high cost. Thus, developing efficient noble-metal-free electrodes is necessary to achieve sustainable hydrogen societies. Here, we report a technique of graphene encapsulation of NiMo alloys for realizing both high catalytic activity and high chemical stability in non-noble metal anodes in transition metal impurities-free aqueous KOH electrolyte. Electrochemical analysis showed that graphene encapsulation significantly enhanced the oxygen evolution reaction (OER) activities of the NiMo anodes and provided long electrode lifetimes and performances comparable to those of commercially available anodes. Density functional theory calculation revealed that graphene encapsulation significantly reduced the adsorption energy of intermediates onto the NiMo surface, thereby remarkably enhancing the OER activity. The graphene encapsulation method provides a promising electrode design to improve the performance in water splitting electrolyzers.

Bimetallic alloys are important catalysts with enhanced catalytic activities and product selectivities. However, the phase dependence of catalytic activity in bimetallic alloys afford contradictory characters in that one phase catalyzes the main reaction and the other catalyzes the side reaction; this aspect of bimetallic alloy catalysts has not been investigated. In this study, we systematically synthesized NiSn alloys from Ni, which is catalytically active in hydrogen generation, and Sn, which is catalytically active in electrochemical CO2 reduction. The thus-prepared alloys were applied in catalyzing the phase-dependent electrochemical CO2 reduction, and the formate generation mechanism was elucidated. The Faradaic efficiency of formate was found to increase with increasing Sn atomic concentration, and Ni3Sn4 showed higher catalytic activity than only Sn for electrochemical CO2 reduction. Density functional theory calculations revealed that Ni can additionally provide catalytically active sites for formate generation in a suitable phase. Thus, our investigation brings a better understanding of the catalytic activities of bimetallic alloys prepared from metals with different characters for electrochemical CO2 reduction.

Accelerating the CO2-recycling process is crucial for preventing global warming. Electrochemical reduction allows the efficient conversion of CO2 into useful chemical compounds with catalysts. During the electrolytic synthesis of CO2, an increase in voltage accelerates the synthesis of the target product and enhances byproduct formation. Previously investigated electrocatalysts do not increase the formation rate with parameter tuning. Herein, we report the development of a polymer-covered Sn catalyst using CO2-absorbable polyethylene glycol (PEG) polymers for the electrochemical reduction of CO2. The catalyst demonstrates high Faradaic efficiencies and doubles the formation rate at −1.2 V (vs RHE) in comparison with that of Sn catalysts. A mechanistic investigation using density functional theory suggests that PEG captures the CO2 molecules and, subsequently, the adsorbed CO2 molecules are transferred to the underlying Sn surface with a low energy barrier. Tuning of the PEG density is vital for a continuous CO2 capture and transfer mechanism that can enhance the catalytic activity.