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Perovskite oxides (ABO₃) have been widely recognized as a class of promising noble-metal–free electrocatalysts due to their unique compositional flexibility and structural stability. Surprisingly, investigation into their size-dependent electrocatalytic properties, in particular barium titanate (BaTiO₃), has been comparatively few and limited in scope. Herein, we report the scrutiny of size- and dopant-dependent oxygen reduction reaction (ORR) activities of an array of judiciously designed pristine BaTiO₃ and doped BaTiO₃ (i.e., La- and Co-doped) nanoparticles (NPs). Specifically, a robust nanoreactor strategy, based on amphiphilic star-like diblock copolymers, is employed to synthesize a set of hydrophobic polymer-ligated uniform BaTiO₃ NPs of different sizes (≤20 nm) and controlled compositions. Quite intriguingly, the ORR activities are found to progressively decrease with the increasing size of BaTiO₃ NPs. Notably, La- and Co-doped BaTiO₃ NPs display markedly improved ORR performance over the pristine counterpart. This can be attributed to the reduced limiting barrier imposed by the formation of -OOH species during ORR due to enhanced adsorption energy of intermediates and the possibly increased conductivity as a result of change in the electronic states as revealed by our density functional theory–based first-principles calculations. Going beyond BaTiO₃ NPs, a variety of other ABO₃ NPs with tunable sizes and compositions may be readily accessible by exploiting our amphiphilic star-like diblock copolymer nanoreactor strategy. They could in turn provide a unique platform for both fundamental and practical studies on a suite of physical properties (dielectric, piezoelectric, electrostrictive, catalytic, etc.) contingent upon their dimensions and compositions.

The development of catalysts with high activity and durability for the cathodicoxygen reduction reaction （ORR） in both alkaline and acidic media is importantfor improving the performance of the proton exchange membrane （PEM） fuelcells. This can be achieved by dispersing Pt-based alloy nanoparticles insideN-doped porous carbon frameworks. However, it still requires the developmentof a facile method towards synthesizing this unique hybrid structure. In this work,we demonstrate that N-doped carbon-stabilized PtCo nanoparticles （PtCo@NC）can be facilely synthesized via thermal decomposition of Pt-incorporatedCo-based zeolitic imidazolate framework （Pt@ZIF-67）. The thickness of the carbonframework can be optimized to enable excellent durability, in sharp contrastto a commercial Pt/C catalyst. The mass activities achieved by optimizing thethickness of the carbon framework are 0.80 and 0.82 A-mg^-1, at 0.9 V vs. RHE inalkaline and acidic electrolytes, respectively, which are nearly 8 times greaterthan those of the Pt/C. This work provides an alternative approach to low-costand high-verformance catalvsts for both alkaline and acidic fuel cells.

Iron-based nanostructures represent an emerging class of catalysts with high electroactivity for oxygen reduction reaction (ORR) in energy storage and conversion technologies. However, current practical applications have been limited by insufficient durability in both alkaline and acidic environments. In particular, limited attention has been paid to stabilizing iron-based catalysts by introducing additional metal by the alloying effect. Herein, we report bimetallic Fe 2 Mo nanoparticles on N-doped carbon (Fe 2 Mo/NC) as an efficient and ultra-stable ORR electrocatalyst for the first time. The Fe 2 Mo/NC catalyst shows high selectivity for a four-electron pathway of ORR and remarkable electrocatalytic activity with high kinetics current density and half-wave potential as well as low Tafel slope in both acidic and alkaline medias. It demonstrates excellent long-term durability with no activity loss even after 10,000 potential cycles. Density functional theory (DFT) calculations have confirmed the modulated electronic structure of formed Fe 2 Mo, which supports the electron-rich structure for the ORR process. Meanwhile, the mutual protection between Fe and Mo sites guarantees efficient electron transfer and long-term stability, especially under the alkaline environment. This work has supplied an effective strategy to solve the dilemma between high electroactivity and long-term durability for the Fe-based electrocatalysts, which opens a new direction of developing novel electrocatalyst systems for future research.

Exploring efficient and cost-effective catalysts to replace precious metal catalysts, such as Pt, for electrocatalytic oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) holds great promise for renewable energy technologies. Herein, we prepare a type of Co catalyst with single-atomic Co sites embedded in hierarchically ordered porous N-doped carbon (Co-SAS/HOPNC) through a facile dual-template cooperative pyrolysis approach. The desirable combination of highly dispersed isolated atomic Co-N₄ active sites, large surface area, high porosity, and good conductivity gives rise to an excellent catalytic performance. The catalyst exhibits outstanding performance for ORR in alkaline medium with a half-wave potential (E 1/2) of 0.892 V, which is 53 mV more positive than that of Pt/C, as well as a high tolerance of methanol and great stability. The catalyst also shows a remarkable catalytic performance for HER with distinctly high turnover frequencies of 0.41 and 3.8 s−1 at an overpotential of 100 and 200 mV, respectively, together with a long-term durability in acidic condition. Experiments and density functional theory (DFT) calculations reveal that the atomically isolated single Co sites and the structural advantages of the unique 3D hierarchical porous architecture synergistically contribute to the high catalytic activity.

Transition metal dichalcogenides (TMDs) are recognized for their exceptional energy storage capabilities and electrochemical potential, stemming from their unique electronic structures and physicochemical properties. In this study, we focus on chromium disulfide (CrS2) as the primary research subject and employ a combination of density functional theory (DFT) and first-principle calculations to investigate the effects of incorporating transition metal elements onto the surface of CrS2. This approach aims to develop a class of bifunctional single-atom catalysts with high efficiency and to analyze their catalytic performance in detail. Theoretical calculations reveal that the Au@CrS2 single-atom catalyst demonstrates outstanding catalytic activity, with a low overpotential of 0.34 V for the oxygen evolution reaction (OER) and 0.37 V for the oxygen reduction reaction (ORR). These results establish Au@CrS2 as a highly effective bifunctional catalyst. Moreover, the catalytic performance of Au@CrS2 surpasses that of traditional commercial catalysts, such as Pt (0.45 V) and IrO2 (0.56 V), suggesting its potential to replace these materials in fuel cells and other energy applications. This study provides a novel approach to the design and development of advanced transition metal-based catalytic materials.

It is still a grand challenge to develop a highly efficient nonprecious-metal electrocatalyst to replace the Pt-based catalysts for oxygen reduction reaction (ORR). Here, we propose a surfactant-assisted method to synthesize single-atom iron catalysts (SA-Fe/NG). The halfwave potential of SA-Fe/NG is only 30 mV less than 20% Pt/C in acidic medium, while it is 30 mV superior to 20% Pt/C in alkaline medium. Moreover, SA-Fe/NG shows extremely high stability with only 12 mV and 15 mV negative shifts after 5,000 cycles in acidic and alkaline media, respectively. Impressively, the SA-Fe/NG-based acidic proton exchange membrane fuel cell (PEMFC) exhibits a high power density of 823 mW cm−2. Combining experimental results and density-functional theory (DFT) calculations, we further reveal that the origin of high-ORR activity of SA-Fe/NG is from the Fe-pyrrolic-N species, because such molecular incorporation is the key, leading to the active site increase in an order of magnitude which successfully clarifies the bottleneck puzzle of why a small amount of iron in the SA-Fe catalysts can exhibit extremely superior ORR activity.

The controllable construction of non-noble metal based bifunctional catalysts with high activities towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of great significance, but remains a challenge. Herein, we reported an effective method to synthesize cobalt-nitrogen doped mesoporous carbon-based bifunctional oxygen electrocatalyst with controllable phosphorus content (Co-N-P X -MC, X = 0.5, 1.0, 1.5, 2.0). The mesoporous carbon substrate endowed the as-prepared samples with more exposed active surface (236.50 m 2 ·g −1 ) and the most appropriate doping ratio of phosphorus had been investigated to be 1.5 (Co-N-P 1.5 -MC). For ORR, Co-N-P 1.5 -MC exhibited excellent catalytic activity with more positive onset potential (1.01 V) and half-wave potential (0.84 V) than the other samples. For OER, Co-N-P 1.5 -MC also showed a low overpotential of 415 mV. Combining experimental results and density-functional theory (DFT) calculations, the outstanding bifunctional catalytic performance of Co-N-P 1.5 -MC was due to the synergistic cooperation between the P and N dopants, which could reduce the reaction barriers and was favorable for ORR and OER. Moreover, the Zn-air battery using Co-N-P 1.5 -MC as the cathode showed remarkable battery performance with high stability (could operate stably for over 160 h at 10 mA·cm −2 ) and maximum power density (119 mW·cm −2 ), demonstrating its potential for practical applications. This work could provide significant enlightenment towards the design and construction of bifunctional oxygen electrocatalyst for next-generation electrochemical devices.

Fuel cells are recognized as promising alternatives to existing conventional energy systems for a sustainable future. However, the synthesis of efficient and robust platinum (Pt) based catalysts remains a challenge for practical fuel cell applications. Herein, the Pt3Co/C nanoparticles with about 4.45 nm are firstly prepared by a “pre‐lithiation‐deposition” strategy on C carrier and used as efficient electrocatalysts for cathodic oxygen reduction reaction. Notably, after heat treatment at 600 °C, the obtained Pt3Co/C‐600 catalyst shows excellent mass and specific activities (MA and SA) of 0.69 A mg  Pt-1 ${_{Pt}^{ - 1} }$ and 1.01 mA cm  Pt-2 ${_{Pt}^{ - 2} }$ , respectively, which are more than one order of magnitude higher than that of Pt/C‐600. In particular, after accelerated durability testing with 20k cycles, the durability of the Pt3Co/C‐600 catalyst (98.3 % retention of MA) is much higher than that of Pt3Co/C‐600 without pre‐lithiation (42.5 % retention of MA). The alloying of Pt and Co and the use of “pre‐lithiation” to enable strong interactions between the carbon carriers and the Pt‐Co nanoparticles contributed to the increased activity and excellent stability. This work provides a new perspective for the development of high‐performance and low‐cost Pt alloy electrocatalysts. The synthesis of efficient and robust platinum‐based catalysts remains a challenge for practical fuel cell applications. In this study, Pt3Co/C nanoparticles about 4.45 nm in size are prepared by a prelithiation‐deposition strategy and used as efficient electrocatalysts for the cathodic oxygen reduction reaction.

Platinum group metal–free (PGM-free) metal-nitrogen-carbon catalysts have emerged as a promising alternative to their costly platinum (Pt)–based counterparts in polymer electrolyte fuel cells (PEFCs) but still face some major challenges, including (i) the identification of the most relevant catalytic site for the oxygen reduction reaction (ORR) and (ii) demonstration of competitive PEFC performance under automotive-application conditions in the hydrogen (H₂)–air fuel cell. Herein, we demonstrate H₂-air performance gains achieved with an iron-nitrogen-carbon catalyst synthesized with two nitrogen precursors that developed hierarchical porosity. Current densities recorded in the kinetic region of cathode operation, at fuel cell voltages greater than ∼0.75 V, were the same as those obtained with a Pt cathode at a loading of 0.1 milligram of Pt per centimeter squared. The proposed catalytic active site, carbon-embedded nitrogen-coordinated iron (FeN₄), was directly visualized with aberration-corrected scanning transmission electron microscopy, and the contributions of these active sites associated with specific lattice-level carbon structures were explored computationally.

HighlightsGeneral principles for designing atomically dispersed metal-nitrogen-carbon (M–N-C) are briefly reviewed.Strategies to enhance the bifunctional catalytic performance of atomically dispersed M–N-C are summarized.Challenges and perspectives of M–N-C bifunctional oxygen catalysts for Rechargeable zinc-air batteries are discussed.Rechargeable zinc-air batteries (ZABs) are currently receiving extensive attention because of their extremely high theoretical specific energy density, low manufacturing costs, and environmental friendliness. Exploring bifunctional catalysts with high activity and stability to overcome sluggish kinetics of oxygen reduction reaction and oxygen evolution reaction is critical for the development of rechargeable ZABs. Atomically dispersed metal-nitrogen-carbon (M-N-C) catalysts possessing prominent advantages of high metal atom utilization and electrocatalytic activity are promising candidates to promote oxygen electrocatalysis. In this work, general principles for designing atomically dispersed M-N-C are reviewed. Then, strategies aiming at enhancing the bifunctional catalytic activity and stability are presented. Finally, the challenges and perspectives of M-N-C bifunctional oxygen catalysts for ZABs are outlined. It is expected that this review will provide insights into the targeted optimization of atomically dispersed M-N-C catalysts in rechargeable ZABs.