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Maximizing the platinum utilization in electrocatalysts toward oxygen reduction reaction (ORR) is very desirable for large-scale sustainable application of Pt in energy systems. A cost-effective carbon-supported carbon-defect-anchored platinum single-atom electrocatalysts (Pt1 /C) with remarkable ORR performance is reported. An acidic H2 /O2 single cell with Pt1 /C as cathode delivers a maximum power density of 520â mW cm-2 at 80 °C, corresponding to a superhigh platinum utilization of 0.09â gPt kW-1 . Further physical characterization and density functional theory computations reveal that single Pt atoms anchored stably by four carbon atoms in carbon divacancies (Pt-C4 ) are the main active centers for the observed high ORR performance.
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The non-precious metal graphene catalyst doped with Fe-Px are recently proposed as a promising candidate in substituting Pt for catalyzing oxygen reduction reaction (ORR) in fuel cells. Systematic DFT calculations are performed to investigate the catalytic activity and the ORR mechanism on the Fe-Px (x = 1-4) system in acid medium in this work. Our results indicated that the configuration with one Fe and two P atoms codoped at zigzag edge site (Fe-P2-zig-G) is the most stable, in excellent agreement with the experimental observation that the ratio of Fe and P is nearly 1 : 2. The four-electron reduction mechanism for ORR on the Fe-P2-zig-G is via the competing OOH hydrogenation pathways (to form either OH + OH or O + H2O). The rate determining step is the O2 hydrogenation with an energy barrier of 0.43 eV, much smaller that of calculated 0.80 eV for pure Pt. In addition, the highest energy barrier of the studied ORR mechanism is the O2 dissociation with an energy barrier of 0.70 eV, a value also smaller than that of pure Pt. This demonstrated that the zigzag edge site of the Fe-P2 codoped graphene should be active for the ORR.
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This study investigates the enhancement of catalytic activity in single-atom catalysts (SACs) through coordination engineering. By introducing non-metallic atoms (X = N, O, or F) into the basal plane of MoS2 via defect engineering and subsequently anchoring hetero-metallic Ru atoms, we created 10 types of non-metal-coordinated Ru SACs (Ru-X-MoS2). Computations indicate that non-metal atom X significantly modifies the electronic structure of Ru, optimizing the hydrogen evolution reaction (HER). Across acidic, neutral, and alkaline electrolytes, Ru-X-MoS2 catalysts exhibit significantly improved HER performance compared with Ru-MoS2, even surpassing commercial Pt/C catalysts. Among these, the Ru-O-MoS2 catalyst, characterized by its asymmetrically coordinated O2-Ru-S1 active sites, demonstrates the most favorable electrocatalytic behavior and exceptional stability across all pH ranges. Consequently, single-atom coordination engineering presents a powerful strategy for enhancing SAC catalytic performance, with promising applications in various fields.
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Water electro-splitting driven by renewable energy is significant in energy conversion for the development of hydrogen energy sources. The hydrogen evolution reaction (HER) directly generating hydrogen products occurs in cathode catalysis. Over the years, significant progress has been made to boost the HER efficiency by exploratively designing highly active and economical Pt-based electrocatalysts. However, there are still some urgent problems to be solved for Pt-based HER catalysts in more economical alkaline electrolytes, such as the slow kinetics caused by additional hydrolysis dissociation steps, which greatly hinders the practical application. This review systematically summarizes several strategies for optimizing alkaline HER kinetics and provides direct guidelines for the design of highly active Pt-based electrocatalysts. Specifically, the intrinsic HER activity in alkaline water electrolysis can be boosted by accelerating the water dissociation, optimizing the hydrogen binding energy or modulating the spatial dimensions of the electrocatalyst based on the HER mechanism. Finally, we prospect the challenges for the alkaline HER on novel Pt-based electrocatalysts, including the active site study, the HER mechanism exploration and the extensible catalyst preparation technologies.
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Photocatalytic water splitting is a promising method for the production of clean energy and searching for efficient photocatalysts has received extensive attention. Fabricating type-II heterojunctions is an effective approach to improve the photocatalytic efficiency. Based on the band edge positions and lattice parameters, we found that several kinds of monochalcogenide monolayers can be used to fabricate type-II heterojunctions with C2N monolayers. C2N/GaTe and C2N/InTe van der Waals (vdW) heterojunctions were investigated as potential photocatalysts for water splitting by means of first-principles computations. Both are type-II heterojunctions, and could promote the efficient spatial separation of electron-hole pairs. Their band edges straddle water redox potentials, satisfying the requirements for photocatalytic water splitting. Besides, the high carrier mobility of C2N/GaTe and C2N/InTe heterojunctions implies that the transfer of carriers to reactive sites is easy, and the recombination probability of photo-generated carriers is reduced. The Gibbs free energy calculations indicate that C2N/GaTe and C2N/InTe heterojunctions, especially C2N/InTe, exhibit high catalytic performance towards hydrogen and oxygen evolution reactions. Particularly, C2N/InTe exhibits a direct band gap with strong absorption in both visible and near ultraviolet regions, indicating that it is a very promising candidate for photocatalytic water splitting. This work would provide a new idea for the development of type-II heterojunctions for photocatalytic water splitting.
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For the large-scale sustainable implementation of polymer electrolyte membrane fuel cells in vehicles, high-performance electrocatalysts with low platinum consumption are desirable for use as cathode material during the oxygen reduction reaction in fuel cells. Here we report a carbon black-supported cost-effective, efficient and durable platinum single-atom electrocatalyst with carbon monoxide/methanol tolerance for the cathodic oxygen reduction reaction. The acidic single-cell with such a catalyst as cathode delivers high performance, with power density up to 680 mW cm-2 at 80 °C with a low platinum loading of 0.09 mgPt cm-2, corresponding to a platinum utilization of 0.13 gPt kW-1 in the fuel cell. Good fuel cell durability is also observed. Theoretical calculations reveal that the main effective sites on such platinum single-atom electrocatalysts are single-pyridinic-nitrogen-atom-anchored single-platinum-atom centres, which are tolerant to carbon monoxide/methanol, but highly active for the oxygen reduction reaction.
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This corrects the article DOI: 10.1038/ncomms15938.
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Quantum chemical molecular dynamics simulations of graphene growth from small island precursors in different carbon nucleation densities on the Ni(111) surface at high temperatures have been conducted. The results indicate that small islands are not static, i.e. lateral diffusion and vertical fluctuation are frequently observed. In the case of low carbon nucleation density, carbon atoms or small carbon patches diffuse and attach to the edge of the nuclei to expand the size of the growing carbon network. The growth of graphene precursors is accompanied by the corresponding changes in the bonding of nickel atoms with the precipitation of subsurface carbon atoms. This is because the carbon-carbon interaction is stronger than the nickel-carbon interaction. In the case of high carbon nucleation densities, the dominant ripening mechanism depends on different growth stages. In the initial stage, the coalescence of carbon islands takes place via the Smoluchowski ripening mechanism. In the later stage the Smoluchowski ripening process is damped owing to the higher diffusion barrier of larger clusters and the restriction of movement by self-assembled nickel step edges. The cross-linking mechanism eventually takes over by the coalescence of extended polyyne chains between graphene islands. In either case, the Ostwald ripening process is not found in our molecular dynamics simulations due to the stability of carbon-carbon bonds within the islands. These investigations should be instructive to the control of graphene growth in experiments.
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Graphene nucleation from crystalline Ni3C has been investigated using quantum chemical molecular dynamics (QM/MD) simulations based on the self-consistent-charge density-functional tight-binding (SCC-DFTB) method. It was observed that the lattice of Ni3C was quickly relaxed upon thermal annealing at high temperature, resulting in an amorphous Ni3C catalyst structure. With the aid of the mobile nickel atoms, inner layer carbon atoms precipitated rapidly out of the surface and then formed polyyne chains and Y-junctions. The frequent sinusoidal-like vibration of the branched carbon configurations led to the formation of nascent graphene precursors. In light of the rapid decomposition of the crystalline Ni3C, it is proposed that the crystalline Ni3C is unlikely to be a reaction intermediate in the CVD-growth of graphene at high temperatures. However, results present here indicate that Ni3C films can be employed as precursors in the synthesis of graphene with exciting possibility.
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Quantum chemical molecular dynamics simulations of graphene nucleation on the Ni(111) surface show that graphene creates its own step-edge as it forms. This "step-edge self-assembly" is driven by the formation of thermodynamically favorable Ni-C σ-bonds at the graphene edge. This dynamic aspect of the Ni(111) catalyst is in contrast to the commonly accepted view that graphene nucleates on a pre-existing, static catalyst step-edge. Simulations also show that, simply by manipulating the subsurface carbon density, preferential formation of single-layer graphene instead of multi-layer graphene can be achieved on nickel catalysts.