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).