Efficient Electron Transfer Processes and Enhanced Electrocatalytic Activity of Cobalt(II) Porphyrin Anchored on Graphene Oxide

We investigated the electronic perturbation between graphene oxide and cobalt porphyrin to reveal the origin of the enhanced electrocatalytic activity of a hybrid complex using time-resolved spectroscopic measurements and theoretical calculations. The impulsively generated charge-separated state, GO⁻-(Co^IIAPFP)⁺, undergoes fast charge recombination (<10 ps) between GO⁻ and (Co^IIAPFP)⁺ moieties. This fast charge recombination is directly related to the quick neutralization of (Co^IIAPFP)⁺, which shortens the dead time of inactive Co^IIIAPFP after the electrocatalytic reduction reaction. The fast transformation of inactive Co^IIIAPFP to active Co^IIAPFP is an important factor in the enhanced electrocatalytic activity of the hybrid complex.     

直接乙醇燃料电池阳极电催化剂的研究进展

介绍了直接乙醇燃料电池(DEFC)具有无毒,来源丰富的优点,分析了DEFC在Pt上的电催化氧化机理,讨论了DEFC的阳极电催化剂的重要作用;探讨了具有高电催化活性的新型Pt基催化剂、新型非贵金属催化剂、新型催化剂载体、新型的催化剂制备方法等的研究现状;指明了阳极催化剂将是今后DEFC研究和发展的重要方向之一。     

(IrOx – Pt)/Ti bifunctional electrodes for oxygen evolution and reduction

Mixed Ir–Pt electrocatalytic films on Ti metal supports were prepared via a galvanic deposition process. Two types of (Ir – Pt)/Ti electrodes were prepared with different Ir–Pt compositions (Ir/Pt atomic composition ratios of 1.74 and 0.44, based on ICP-MS measurements) and of a similar total metal loading (0.15 and 0.12 mg cm^?2). The simultaneous deposition of both metallic Ir and Pt occurred spontaneously upon immersion of a freshly etched Ti metal substrate into a composite solution of Ir(IV) and Pt(IV) complexes of variable concentration. This was followed by electrochemical anodization to convert Ir to IrO_x. Both electrodes showed homogeneous Ir and Pt dispersion on the Ti surface. The bifunctional electrocatalytic performance of (IrO_x/Ir – Pt)/Ti electrodes has been tested towards the oxygen evolution (OER) and reduction (ORR) reactions in acidic solutions. The thus prepared Ti-supported Ir–Pt film electrodes exhibited satisfactory performance towards both reactions, with mass-specific currents for OER being higher than those at a single component IrOx/Ir/Ti electrode and the ones for ORR being comparable to those at a single component Pt/Ti electrode.     

Introduction of a new active and stable cathode catalyst based on bimetal-organic frameworks/PPy-sheet for alkaline direct ethanol fuel cell

For the first time, the polypyrrole (PPy) with a sheet-like structure was synthesized by a high-efficiency and facile chemical reaction process. A new composite with the growth of bimetallic zeolitic imidazolate frameworks on polypyrrole sheet-like (BMZIF@PPy) was synthesized. Then, the BMZIF@PPy composite by different heat-treatment temperatures is applied to make oxygen reduction reaction (ORR) electrocatalysts. Electrochemical measurements perform to investigate the ORR properties in both acidic and alkaline media. The onset potential and the limiting current density for the Cobalt/Zinc-nanocarbon@polypyrrole pyrolysis at 800 °C (Co/Zn-NC@PPy-800) were 0.977 V_RHE and 4.99 mA cm^?2 in 0.1 M KOH and 0.85V_RHE and 5.48 mA cm^?2 in 0.5 M H₂SO₄. Finally, due to the good activity and stability in alkaline media, the Co/Zn-NC@PPy-800 electrocatalyst is used as the cathode in an alkaline direct ethanol fuel cell. The maximum power of the Co/Zn-NC@PPy-800 cathode catalyst was 77% higher than that of the commercial Pt/C electrocatalyst.     

Metastable Phase Cu with Optimized Local Electronic State for Efficient Electrocatalytic Production of Ammonia from Nitrate

Electrocatalytic nitrate (NO₃⁻) reduction reaction (NITRR) is an inspiring route for ammonia (NH₃) synthesis at ambient condition. The metallic Cu-based material with low cost and high activity is one of the most promising electrocatalysts for NITRR. However, due to the weaker atomic H^*-providing capacity, the produced intermediate—nitrite tends to accumulate on its surface, leading to unsatisfactory NH₃ selectivity and Faradic efficiency (FE). Herein, a novel and facile O₂/Ar plasma oxidation and subsequent electro-reduction strategy is developed to synthesize a kind of metastable phase Cu. Excitingly, the metastable phase Cu demonstrates superior NITRR performance to conventional phase Cu with high NH₄⁺ selectivity (97.8%) and FE (99.8%). Density function theory (DFT) calculations reveal that the upshift of the d-band center to near the Fermi level in metastable phase Cu contributes to the enhanced activity, while the relatively strong adsorption of H^* facilitates the conversion from NO₂^*/NO^* to NOOH^*/NOH^* and thus ensures high selectivity and FE. Furthermore, when evaluated as cathode material in Zn-NO₃⁻ battery, high power density (7.56 mW cm⁻²) and NH₄⁺ yield (76 µmol h⁻¹ cm⁻²) are achieved by the metastable phase Cu-based battery.     

Electrochemical Oxidation of 5-Hydroxymethylfurfural on CeO2-Modified Co3O4 with Regulated Intermediate Adsorption and Promoted Charge Transfer

Electrocatalytic 5-hydroxymethylfurfural oxidation reaction (HMFOR) can replace the kinetically slow oxygen evolution reaction to yield high value-added chemicals. In this study, interface engineering is constructed by modifying CeO₂ nanoparticles on Co₃O₄ nanowires supported by nickel foam (NF). The construction of the heterointerface can facilitate the structural evolution of catalysts and charge transfer, as a result, the successfully synthesized NF@Co₃O₄/CeO₂ exhibits higher 5-hydroxymethylfurfural conversion (98.0%), 2,5-furandicarboxylic acid (FDCA) yield (94.5%), and Faradaic efficiency (97.5%) at a low electrolysis potential of 1.40 V_RHE compared to NF@Co₃O₄ and NF@CeO₂. Density-functional theory calculations indicate that the establishment of heterointerface can effectively regulate the intermediate adsorption and promote electron transfer, which greatly reduces the activation energy of the dehydrogenation step in 5-formyl-2-furancarboxylic acid (FFCA), and promotes the further oxidation of FFCA to FDCA, thereby improving the performance of HMFOR. In this study, the HMFOR behavior of the Co₃O₄/CeO₂ interface effect is deeply explored, which provides guidance for the future design of heterointerface catalysts with efficient HMFOR performance.     

Facile Synthesis of Medium-Entropy Metal Sulfides as High-Efficiency Electrocatalysts toward Oxygen Evolution Reaction

Developing highly efficient and durable electrocatalysts toward oxygen evolution reaction (OER) is an urgent demand to produce clean hydrogen energy. In this study, a series of medium-entropy metal sulfides (MEMS) of (NiFeCoX)₃S₄ (where X = Mn, Cr, Zn) are synthesized by a facile one-pot solvothermal strategy using molecular precursors. Benefiting from the multiple-metal synergistic effect and the low crystallinity, these MEMS show significantly enhanced electrocatalytic OER activity compared with the binary-metal (NiFe)₃S₄ and ternary-metal (NiFeCo)₃S₄ counterparts. Especially, (NiFeCoMn)₃S₄ delivers a low overpotential of 289 mV at 10 mA cm⁻², a decent Tafel slope of 75.6 mV dec⁻¹ and robust catalytic stability in alkaline medium, outperforming the costly IrO₂ benchmark electrocatalyst and the majority of the reported metal sulfide-based electrocatalysts until now. These MEMS with facile synthesis and excellent electrocatalytic performance bring a great opportunity to design desirable electrocatalysts for practical application.     

Regulating Fe Aggregation State via Unique Fe?N?V Pre-Coordination to Optimize the Adsorption-Catalysis Effect in High-Performance Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) suffer from uncontrollable shuttling behavior of lithium polysulfides (LiPSs: Li₂S_x, 4 ≤ x ≤8) and the sluggish reaction kinetics of bidirectional liquid-solid transformations, which are commonly coped through a comprehensive adsorption-catalysis strategy. Herein, a unique Fe N V pre-coordination is introduced to regulate the content of “dissociative Fe³⁺” in liquid phase, realizing the successful construction of N-doped micro-mesoporous “urchin-like” hollow carbon nanospheres decorated with single atom Fe-N₄ sites and VN nanoparticles (denoted as SA-Fe/VN@NMC). The strong chemisorption ability toward LiPSs and catalyzed Li₂S decomposition behavior on VN, along with the boosted reaction kinetics for sulfur reduction on SA-Fe sites are experimentally and theoretically evidenced. Moreover, the nanoscale-neighborhood distribution of VN and SA-Fe active sites presents synergistic effect for the anchoring-reduction-decomposition process of sulfur species. Thus SA-Fe/VN@NMC presents an optimized adsorption-catalysis effect for the whole sulfur conversion. Therefore, the SA-Fe/VN@NMC based Li-S cells exhibit high cyclic stability (a low decay of 0.024% per cycle over 700 cycles at 1 C, sulfur content: 70 wt%) and considerable rate performance (683.2 mAh g⁻¹ at 4 C). Besides, a high areal capacity of 5.06 mAh cm⁻² is retained after 100 cycles under the high sulfur loading of 5.6 mg cm⁻². This work provides a new perspective to design the integrated electrocatalysts comprising hetero-formed bimetals in LSBs.     

Approaching Elaborate Control of the Nano-Products of Carbothermal Reduction Reaction Through In Situ Identification

Atomic understanding of a chemical reaction can realize the programmable design and synthesis of desired products with specific compositions and structures. Through directly monitoring the phase transition and tracking the dynamic evolution of atoms in a chemical reaction, in situ transmission electron microscopy (TEM) techniques offer the feasibility of revealing the reaction kinetics at the atomic level. Nevertheless, such investigation is quite challenging, especially for reactions involving multi-phase and complex interfaces, such as the widely adopted carbothermal reduction (CTR) reactions. Herein, in-situ TEM is applied to monitor the CTR of Co₃O₄ nanocubes on reduced graphene oxide nanosheets. Together with the first-principle calculation, the migration route of Co atoms during the phase transition of the CTR reaction is revealed. Meanwhile, the interfacial edge-dislocations/stress-gradient is identified as a result of the atomistic diffusion, which in turn can affect the morphology variation of the reactants. Accordingly, controllable synthesis of Co-based nanostructure with a desirable phase and structure has been achieved. This work not only provides atomic kinetic insight into CTR reactions but also offers a novel strategy for the design and synthesis of functional nanostructures for emerging energy technologies.     

Interstitial Hydrogen Atom to Boost Intrinsic Catalytic Activity of Tungsten Oxide for Hydrogen Evolution Reaction

Tungsten oxide (WO₃) is an appealing electrocatalyst for the hydrogen evolution reaction (HER) owing to its cost-effectiveness and structural adjustability. However, the WO₃ electrocatalyst displays undesirable intrinsic activity for the HER, which originates from the strong hydrogen adsorption energy. Herein, for effective defect engineering, a hydrogen atom inserted into the interstitial lattice site of tungsten oxide (H_0.23WO₃) is proposed to enhance the catalytic activity by adjusting the surface electronic structure and weakening the hydrogen adsorption energy. Experimentally, the H_0.23WO₃ electrocatalyst is successfully prepared on reduced graphene oxide. It exhibits significantly improved electrocatalytic activity for HER, with a low overpotential of 33 mV to drive a current density of 10 mA cm⁻² and ultra-long catalytic stability at high-throughput hydrogen output (200 000 s, 90 mA cm⁻²) in acidic media. Theoretically, density functional theory calculations indicate that strong interactions between interstitial hydrogen and lattice oxygen lower the electron density distributions of the d-orbitals of the active tungsten (W) centers to weaken the adsorption of hydrogen intermediates on W-sites, thereby sufficiently promoting fast desorption from the catalyst surface. This work enriches defect engineering to modulate the electron structure and provides a new pathway for the rational design of efficient catalysts for HER.