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Development of efficient catalysts for electrochemical carbon dioxide reduction reaction (CO2RR) represents a great challenge in renewable energy research. Although noble metals have long been explored as catalysts for CO2RR, their reactivity and selectivity remain rather low owing to the competing hydrogen evolution reaction (HER). Here, this work proposes that noble metal monolayers (MLs) supported by transition metal carbides (TMCs) and nitrides (TMNs) can become exceptional CO2RR catalysts with much suppressed HER. This work shows that there is a direct, antibonding interaction between the hydrogen adsorbate and the TMC/TMN substrates, while such interactions between CO2RR intermediates and the substrates are absent. This difference enables dual‐site functionalization of the ML catalysts, which circumvents the energy scaling relations dictating the competition between CO2RR and HER. Consequently, it is possible to reduce the binding of the H adsorbate to suppress HER and simultaneously increase the binding of CO2RR intermediates to boost the CO2RR. This work identifies several Ag and Au‐based catalysts that are thermodynamically and electrochemically stable and exhibit high activity and selectivity toward the production of formic acid. In addition, this work predicts that higher order CO2RR products including methanol and ethylene can also be produced on selected catalysts. [ABSTRACT FROM AUTHOR]

CO 2 electroreduction, dual-site reactions, first-principles calculations, metal monolayer catalysts Keywords: CO 2 electroreduction; dual-site reactions; first-principles calculations; metal monolayer catalysts EN CO 2 electroreduction dual-site reactions first-principles calculations metal monolayer catalysts 1 1 1 01/27/23 20230120 NES 230120 B CO SB 2 sb Electroreduction b In article number 2203138, Zhonglong Zhao and Gang Lu predict that noble metal monolayers supported by transition metal carbides (TMCs) and nitrides (TMNs) could be selective catalysts for the carbon dioxide reduction reaction with suppressed hydrogen evolution reaction. Dual-Site Functionalization on Supported Metal Monolayer Electrocatalysts for Selective CO2 Reduction (Adv. [Extracted from the article]

PtM alloy catalysts (e.g., PtFe, PtCo), especially in an intermetallic L10 structure, have attracted considerable interest due to their respectable activity and stability for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, metal‐catalyzed formation of ·OH from H2O2 (i.e., Fenton reaction) by Fe‐ or Co‐containing catalysts causes severe degradation of PEM/catalyst layers, hindering the prospects of commercial applications. Zinc is known as an antioxidant in Fenton reaction, but is rarely alloyed with Pt owing to its relatively negative redox potential. Here, sub‐4 nm intermetallic L10‐PtZn nanoparticles (NPs) are synthesized as high‐performance PEMFC cathode catalysts. In PEMFC tests, the L10‐PtZn cathode achieves outstanding activity (0.52 A mgPt−1 at 0.9 ViR‐free, and peak power density of 2.00 W cm−2) and stability (only 16.6% loss in mass activity after 30 000 voltage cycles), exceeding the U.S. DOE 2020 targets and most of the reported ORR catalysts. Density function theory calculations reveal that biaxial strains developed upon the disorder‐order (A1L10) transition of PtZn NPs would modulate the surface PtPt distances and optimize PtO binding for ORR activity enhancement, while the increased vacancy formation energy of Zn atoms in an ordered structure accounts for the improved stability. [ABSTRACT FROM AUTHOR]

Abstract: Lead tri‐iodide methylammonium (MAPbI3) perovskite polycrystalline materials show complex optoelectronic behavior, largely because their 3D semiconducting inorganic framework is strongly perturbed by the organic cations and ubiquitous structural or chemical inhomogeneities. Here, a newly developed time‐dependent density functional theory‐based theoretical formalism is taken advantage of. It treats electron–hole and electron–nuclei interactions on the same footing to assess the many‐body excited states of MAPbI3 perovskites in their pristine state and in the presence of point chemical defects. It is shown that lead and iodine vacancies yield deep trap states that can be healed by dynamic effects, namely rotation of the methylammonium cations in response to point charges, or through slight changes in chemical composition, namely by introducing a tiny amount of chlorine dopants in the defective MAPbI3. The theoretical results are supported by photoluminescence experiments on MAPbI3−mClm and pave the way toward the design of defect‐free perovskite materials with optoelectronic performance approaching the theoretical limits. [ABSTRACT FROM AUTHOR]

Engineering the crystal structure of Pt–M (M = transition metal) nanoalloys to chemically ordered ones has drawn increasing attention in oxygen reduction reaction (ORR) electrocatalysis due to their high resistance against M etching in acid. Although Pt–Ni alloy nanoparticles (NPs) have demonstrated respectable initial ORR activity in acid, their stability remains a big challenge due to the fast etching of Ni. In this work, sub‐6 nm monodisperse chemically ordered L10‐Pt–Ni–Co NPs are synthesized for the first time by employing a bifunctional core/shell Pt/NiCoOx precursor, which could provide abundant O‐vacancies for facilitated Pt/Ni/Co atom diffusion and prevent NP sintering during thermal annealing. Further, Co doping is found to remarkably enhance the ferromagnetism (room temperature coercivity reaching 2.1 kOe) and the consequent chemical ordering of L10‐Pt–Ni NPs. As a result, the best‐performing carbon supported L10‐PtNi0.8Co0.2 catalyst reveals a half‐wave potential (E1/2) of 0.951 V versus reversible hydrogen electrode in 0.1 m HClO4 with 23‐times enhancement in mass activity over the commercial Pt/C catalyst along with much improved stability. Density functional theory (DFT) calculations suggest that the L10‐PtNi0.8Co0.2 core could tune the surface strain of the Pt shell toward optimized Pt–O binding energy and facilitated reaction rate, thereby improving the ORR electrocatalysis. [ABSTRACT FROM AUTHOR]

Cathode materials with high energy density, long cycle life, and low cost are of top priority for energy storage systems. The Li‐rich transition metal (TM) oxides achieve high specific capacities by redox reactions of both the TM and oxygen ions. However, the poor reversible redox reaction of the anions results in severe fading of the cycling performance. Herein, the vacancy‐containing Na4/7[Mn6/7(◻Mn)1/7]O2 (◻Mn for vacancies in the MnO slab) is presented as a novel cathode material for Na‐ion batteries. The presence of native vacancies endows this material with attractive properties including high structural flexibility and stability upon Na‐ion extraction and insertion and high reversibility of oxygen redox reaction. Synchrotron X‐ray absorption near edge structure and X‐ray photoelectron spectroscopy studies demonstrate that the charge compensation is dominated by the oxygen redox reaction and Mn3+/Mn4+ redox reaction separately. In situ synchrotron X‐ray diffraction exhibits its zero‐strain feature during the cycling. Density functional theory calculations further deepen the understanding of the charge compensation by oxygen and manganese redox reactions and the immobility of the Mn ions in the material. These findings provide new ideas on searching for and designing materials with high capacity and high structural stability for novel energy storage systems. A novel air‐stable layer‐structured Mn‐based oxide Na4/7[Mn6/7(◻Mn)1/7]O2 is presented. The presence of native vacancies gives this material high structural flexibility and stability upon Na‐ion extraction and insertion and enables high reversibility of oxygen redox reactions. The findings provide new ideas for selecting and designing new cathode materials with high capacity and structural stability. [ABSTRACT FROM AUTHOR]

The Li‐rich layer‐structured oxides are regarded as one of the most promising cathode materials for their high energy density but suffer from severe problems such as capacity fading, poor rate performance, and continuous potential dropping. These issues are addressed here by surface doping of niobium (Nb) and other heavy ions in a Li‐rich Mn‐based layered oxide, Li1.2Mn0.54Ni0.13Co0.13O2. The doped ions are verified to be located in the Li‐layer near the oxide surface; they bind the slabs via the strong NbO bonds and "inactivate" the surface oxygen, enhancing the structural stability. The specific capacity of the modified oxide reaches 320 mAh g−1 in the initial cycle, 94.5% of which remains after 100 cycles. More importantly, the average discharge potential drops only by 136 mV in this process. The findings of this study illustrate the importance of inactivating the surface oxygen in suppressing the cation mixing in the bulk, providing an effective strategy for designing high‐performance Li‐rich cathode materials. A new strategy is proposed to improve the electrochemical and thermal performance of Li‐rich layered oxide by niobium (Nb) surface doping. Transformation from layered to rocksalt‐like structure is stopped and the potential becomes stable by inactivating surface oxygen in Li1.2Mn0.54Ni0.13Co0.13O2. These findings serve as a revelation for the development of Li‐rich layered materials with mitigated potential decay and a longer lifespan. [ABSTRACT FROM AUTHOR]