Fe?N?C Electrocatalysts with Densely Accessible Fe?N4 Sites for Efficient Oxygen Reduction Reaction

The development of iron and nitrogen co-doped carbon (Fe N C) electrocatalysts for the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells (PEMFCs) is a grand challenge due to the low density of accessible Fe N₄ sites. Here, an in situ trapping strategy using nitrogen-rich molecules (e.g., melamine, MA) is demonstrated to enhance the amount of accessible Fe N₄ sites in Fe N C electrocatalysts. The melamine molecules can participate in the coordination of Fe ions in zeolitic imidazolate frameworks to form Fe N₆ sites within precursors. These Fe N₆ sites are then converted into atomically dispersed Fe N₄ sites during a pyrolytic process. Remarkably, the Fe N C/MA exhibits a high single-atom Fe content (3.5 wt.%), a large surface area (1160 m² g⁻¹), and a high density of accessible FeN₄ sites (45.7 × 10¹⁹ sites g⁻¹). As a result, Fe N C/MA shows a much enhanced ORR activity with a half-wave potential of 0.83 V (vs the reversible hydrogen electrode) in a 0.5 m H₂SO₄ electrolyte solution and a good performance in a PEMFC system with an activity of 80 mA cm⁻² at 0.8 V under 1.0 bar H₂/air. This work offers a promising approach toward high-performance carbon-based ORR electrocatalysts.     

Substitutionally Dispersed High-Oxidation CoOx Clusters in the Lattice of Rutile TiO2 Triggering Efficient Co?Ti Cooperative Catalytic Centers for Oxygen Evolution Reactions

The development of economical, highly active, and robust electrocatalysts for oxygen evolution reaction (OER) is one of the major obstacles for producing affordable water splitting systems and metal-air batteries. Herein, it is reported that the subnanometric CoO_x clusters with high oxidation state substitutionally dispersed in the lattice of rutile TiO₂ support (Co-TiO₂) can be prepared by a thermally induced phase segregation process. Owing to the strong interaction of CoO_x clusters and TiO₂ support, Co-TiO₂ exhibits both excellent intrinsic activity and durability for OER. The turnover frequency of Co-TiO₂ is up to 3.250 s⁻¹ at overpotentials of 350 mV; this value is one of the highest in terms of OER performance among the current Co-based active materials under similar testing conditions; moreover, the OER current density loss is only 6.5% at a constant overpotential of 400 mV for 30 000 s, which is superior to the benchmark Co₃O₄ and RuO₂ catalysts. Mechanism analysis demonstrates that charge transfer occurs between Co sites and their neighboring Ti atoms, triggering the efficient Co Ti cooperative catalytic centers, in which OH* and O* are preferred to be adsorbed on the bridging sites of Co and Ti with favorable adsorption energy, inducing a lower energy barrier for O₂ generation.     

V “Bridged” Co?O to Eliminate Charge Transfer Barriers and Drive Lattice Oxygen Oxidation during Water-Splitting

Oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) play significant role on the practical applications of water splitting for producing clean fuel. Although some low-cost metal oxides are active on catalyzing OER and HER, the instinct drawback of sluggish charges carriers transfer mobility decrease the reactions kinetic and hinder their application. To overcome the issue, Co V oxide is successfully built-up with a Co O V structure to eliminate energy barrier during carriers transfer by the spin-flip hopping process, which can be coated on various substrate to stimulate OER and HER. Moreover, the V “bridge” between Co O bonds stimulates the OER through more effective lattice oxygen oxidation mechanism, which can directly format O O bond in more effective pathway. The protocol could be spread on rational design of such OER electrocatalysts on various electrode to lower-cost water splitting.     

Rechargeable Li?CO2 Batteries with Graphdiyne as Efficient Metal-Free Cathode Catalysts

A rechargeable Li CO₂ battery is one of the promising power sources for utilizing the greenhouse gas CO₂ in a sustainable approach. However, highly efficient catalysts for reversible formation/decomposition of insulating discharge product, Li₂CO₃, are the main challenge, which can boost the cycle stability. Herein, 2D single-atom-thick graphdiyne (GDY) with abundant acetylenic bond sites is prepared by a bottom-up cross-coupling reaction strategy and used as metal-free catalysts for reversible Li CO₂ batteries. The prepared GDY has a rich diacetylenic unit and atomic-level in-plane pores in the network, which can chemically adsorb the CO₂ molecules and easily promote the Li⁺ diffusion and thereby resulting in uniform nucleation and reversible formation/decomposition of the discharge product. The GDY hybrid cathodes show a small overpotential gap of 1.4 V at a current density of 50 mA · g⁻¹, a high full discharge capacity of 18 416 mAh · g⁻¹ at 100 mA · g⁻¹, and outstanding long-term stability of 158 cycles at 400 mA · g⁻¹ with a curtailing capacity of 1000 mAh · g⁻¹. Furthermore, a flexible belt-shaped Li CO₂ battery is fabricated as a proof of concept with a high gravimetric energy density of 165.5 Wh · kg⁻¹ (based on the mass of the whole device) as well as excellent mechanical flexibility.     

NiMoO4 Nanosheets Anchored on N?S Doped Carbon Clothes with Hierarchical Structure as a Bidirectional Catalyst toward Accelerating Polysulfides Conversion for Li?S Battery

The serious shuttle effect, sluggish reduction kinetics of polysulfides and the difficult oxidation reaction of Li₂S have hindered Li S battery practical application. Herein, a 3D hierarchical structure composed of NiMoO₄ nanosheets in situ anchored on N S doped carbon clothes (NiMoO₄@NSCC) as the free-standing host is creatively designed and constructed for Li S battery. Dual transitional metal oxide (NiMoO₄) increases the electrons density near the Fermi level due to the contribution of the incorporating molybdenum (Mo), leading to the smaller bandgap, and thus stronger metallic properties compared with NiO. Furthermore, as a bidirectional catalyst, NiMoO₄ is proposed to facilitate reductions of polysulfides through lengthening the S S bond distance of Li₂S₄ and reducing the free energy of polysulfides conversion, meanwhile promote critical oxidation of insulative discharge product (Li₂S) via lengthening Li S bond distance of Li₂S and decreasing Li₂S decomposition barrier. Therefore, after loading sulfur (2 mg cm⁻²), NiMoO₄@NSCC/S as the self-supporting cathode for the Li S battery exhibits impressive long cycle stability. This study proposes a concept of a bidirectional catalyst with dual metal oxides, which would supply a novel vision to construct the high-performance Li S battery.     

Efficient Electrocatalytic Reduction of CO2 to Ethanol Enhanced by Spacing Effect of Cu?Cu in Cu2-xSe Nanosheets

It is highly desired yet challenging to strategically steer carbon dioxide (CO₂) electroreduction reaction (CO₂ER) toward ethanol (EtOH) with high activity, which provides a promising way for intermittent renewable energy reservation. Controlling spatial distance between the adjoining active centers and promoting the C C coupling progress are crucial to realize this purpose. Herein, ultrathin 2D Cu_2-xSe is prepared with abundant Se vacancies, where the spatial distance between the Cu Cu around the Se vacancies is effectively shortened because of the lattice stress. Besides, the moderate spatial distance induced by Se vacancies can significantly decrease the Gibbs free energy of asymmetric *CO *CHO coupling progress, effectively change the local charge distribution, decrease the valence state of Cu atoms and increase the electron-donating capacity of the dual active sites. Combining experimental observations and density functional theory   simulations, the Cu Cu dual sites with spatial distance of 2.51 Å in V_Se-Cu_2-xSe sample can catalyze CO₂ER to EtOH with high selectivity in a potential range from −0.4 to −1.6 V, and reach the highest faradaic efficiency of 68.1% at −0.8 V. This work reveals the influence of spacing effect on ethanol selectivity, and provides a new idea for future design of catalysts with chain elongation reaction, which can bring extensive attention.     

Unique P?Co?N Surface Bonding States Constructed on g‐C3N4 Nanosheets for Drastically Enhanced Photocatalytic Activity of H2 Evolution

Developing high‐efficiency and low‐cost photocatalysts by avoiding expensive noble metals, yet remarkably improving H₂ evolution performance, is a great challenge. Noble‐metal‐free catalysts containing Co(Fe)? N? C moieties have been widely reported in recent years for electrochemical oxygen reduction reaction and have also gained noticeable interest for organic transformation. However, to date, no prior studies are available in the literature about the activity of N‐coordinated metal centers for photocatalytic H₂ evolution. Herein, a new photocatalyst containing g‐C₃N₄ decorated with CoP nanodots constructed from low‐cost precursors is reported. It is for the first time revealed that the unique P(δ^?)? Co(δ⁺)? N(δ^?) surface bonding states lead to much superior H₂ evolution activity (96.2 µmol h^?1) compared to noble metal (Pt)‐decorated g‐C₃N₄ photocatalyst (32.3 µmol h^?1). The quantum efficiency of 12.4% at 420 nm is also much higher than the record values (≈2%) of other transition metal cocatalysts‐loaded g‐C₃N₄. It is believed that this work marks an important step toward developing high‐performance and low‐cost photocatalytic materials for H₂ evolution.     

Integration of Alloy Segregation and Surface Co?O Hybridization in Carbon-Encapsulated CoNiPt Alloy Catalyst for Superior Alkaline Hydrogen Evolution

Constructing an efficient alkaline hydrogen evolution reaction (HER) catalyst with low platinum (Pt) consumption is crucial for the cost reduction of energy devices, such as electrolyzers. Herein, nanoflower-like carbon-encapsulated CoNiPt alloy catalysts with composition segregation are designed by pyrolyzing morphology-controlled and Pt-proportion-tuned metal–organic frameworks (MOFs). The optimized catalyst containing 15% CoNiPt NFs (15%: Pt mass percentage, NFs: nanoflowers) exhibits outstanding alkaline HER performance with a low overpotential of 25 mV at a current density of 10 mA cm⁻², far outperforming those of commercial Pt/C (47 mV) and the most advanced catalysts. Such superior activity originates from an integration of segregation alloy and Co-O hybridization. The nanoflower-like hierarchical structure guarantees the full exposure of segregation alloy sites. Density functional theory calculations suggest that the segregation alloy components not only promote water dissociation but also facilitate the hydrogen adsorption process, synergistically accelerating the kinetics of alkaline HER. In addition, the activity of alkaline HER is volcanically distributed with the surface oxygen content, mainly in the form of Co_3d O_2p hybridization, which is another reason for enhanced activity. This work provides feasible insights into the design of cost-effective alkaline HER catalysts by coordinating kinetic reaction sites at segregation alloy and adjusting the appropriate oxygen content.