Nitrogen and Oxygen Co-Doping Assisted Synthesis of Highly Dispersed Pd Nanoparticles on Hollow Carbon Spheres as Efficient Electrocatalysts for Oxygen Reduction Reaction

Electrochemical reduction of O₂ (oxygen reduction reaction; ORR) provides an opportunity to achieve the commercial application of clean energy, but it remains challenging, so the rational design of inexpensive and efficient electrocatalysts is required. Palladium-based electrocatalysts have emerged as a class of the most promising candidates for the ORR, which could accelerate O₂ adsorption, dissociation, and electron transfer. However, the metal Pd atoms tend to aggregate into nanoparticles, driven by the tendency of the metal surface free energy to decrease, which significantly reduces the atom utilization efficiency and the catalytic performance. Herein, a facile double solvent impregnation method is developed for the synthesis of highly dispersed Pd nanoparticles supported on hollow carbon spheres (Pd-HCS), which could act as efficient electrocatalysts for the ORR in basic solution. Systematic investigation reveals that the nitrogen-containing and oxygen-containing functional groups (especially −COOH groups) are essential for achieving the homogenous dispersion of Pd nanoparticles. Significantly, the optimized Pd-HCS electrocatalyst with homogeneously dispersed Pd nanoparticles and Pd−N sites delivers high electrocatalytic activity for the ORR and excellent stability, without significant decay in onset potential and half-potential and good resistance to methanol crossover. This work offers a new route for the rational design of efficient ORR electrocatalysts toward advanced materials and emerging applications.     

Core–Shell Pd@M (M=Ni,Cu, Co) Nanoparticles/Graphene Ensembles with High Mass Electrocatalytic Activity Toward the Oxygen Reduction Reaction

Herein, it is demonstrated that pyrene butyric acid (PBA)-stabilized metal nanoparticles with core–shell morphology, Pd@M_NPs (M=Ni, Cu, Co), non-covalently supported on graphene (G) sheets, are more active towards oxygen electroreduction in alkaline environments than the benchmark Pd/C catalyst, albeit with a 70 % lower precious metal loading. The PBA-stabilized Pd@M_NPs (M=Ni, Cu, Co)/G ensembles were prepared by employing a simple modified polyol method and galvanic replacement and thoroughly characterized with advanced microscopy imaging and complementary spectroscopic techniques. Electrochemical studies revealed that Pd@Ni_NPs/G presents the optimum performance, exhibiting a 30 mV more positive onset potential and 3.2 times greater mass activity over Pd/C. Moreover, chronoamperometric assays showed the minimum activity loss for Pd@Ni_NPs/G, not only among its core–shell counterparts but importantly when compared with the benchmark catalyst. The excellent performance of Pd@Ni_NPs/G was attributed to the (a) presence of PBA as stabilizer, (b) uniform Pd@Ni_NPs dispersion onto the graphene sheets, (c) efficient intra-ensemble interactions between the two species, (d) existence of the core–shell structure for Pd@Ni_NPs, and (e) stability of the Ni core metal under the reaction conditions. Last, the oxygen reduction on Pd@Ni_NPs/graphene occurs by the direct four-electron reduction pathway, showing great potential for use in energy related applications.     

Efficient Electrochemical Reduction of CO2 to Formate in Methanol Solutions by Mn-Functionalized Electrodes in the Presence of Amines**

Carbon cloth electrode modified by covalently attaching a manganese organometallic catalyst is used as cathode for the electrochemical reduction of CO₂ in methanol solutions. Six different industrial amines are employed as co-catalyst in millimolar concentrations to deliver a series of new reactive system. While such absorbents were so far believed to provide a CO₂ reservoir and act as sacrificial proton source, we herein demonstrate that this role can be played by methanol, and that the adduct formed between CO₂ and the amine can act as an effector or inhibitor toward the catalyst, thereby enhancing or reducing the production of formate. Pentamethyldiethylentriamine ( PMDETA) , identified as the best effector in our series, converts CO₂ in wet methanolic solution into bisammonium bicarbonate. Computational studies revealed that this adduct is responsible for a barrierless transformation of CO₂ to formate by the reduced form of the Mn catalyst covalently bonded to the electrode surface. As a consequence, selectivity can be switched on demand from CO to formate anion, and in the case of ( PMDETA ) an impressive TON_HCOO− of 2.8×10⁴ can be reached. This new valuable knowledge on an integrated capture and utilization system paves the way toward more efficient transformation of CO₂ into liquid fuel.     

Unraveling the Synergistic Mechanism of Bi-Functional Nickel–Iron Phosphides Catalysts for Overall Water Splitting

Ni–Fe bimetallic electrocatalysts are expected to replace existing precious metal catalysts for water splitting and achieve industrial applications due to their high intrinsic activity and low cost. However, the mechanism by which Ni and Fe species synergistically enhance catalytic activity remains obscure, which still needs further in-depth study. In this study, a highly active bi-functional electrocatalyst of Ni₂P/FeP heterostructures is constructed on Fe foam (Ni₂P/FeP-FF), clearly illustrating the effect of Ni on Fe species for oxygen evolution reaction (OER) and revealing the true catalytic active phase for hydrogen evolution reaction (HER). The Ni₂P/FeP-FF only needs overpotentials of 217 and 42 mV to reach 10 mA cm⁻² for OER and HER, respectively, exhibiting superior bi-functional activity for overall water splitting. The Ni can elevate the strength of Fe O on Ni₂P/FeP-FF surface and promote the formation of high-valence FeOOH phase during OER, thus enhancing OER performance. Based on first-principles calculations and Raman characterizations, the Ni₂P/Ni(OH)₂ heterojunction evolved from Ni₂P/FeP is identified as the real high active phase for HER. This study not only builds a near-commercial bifunctional electrocatalyst for overall water splitting, but also provides a deep insight for synergistic catalytic mechanism of Ni and Fe species.     

Modulating Local Interfacial Bonding Environment of Heterostructures for Energy-Saving Hydrogen Production at High Current Densities

Coupling urea oxidation reaction (UOR) with hydrogen evolution reaction (HER) is an effective energy-saving technique for hydrogen generation. However, exploring efficient bifunctional electrocatalysts under high current density is still challenging. Herein, hierarchical Fe doped cobalt selenide coupled with FeCo layered double hydroxide (Fe-Co_0.85Se/FeCo LDH) array as a self-supported superior bifunctional heterojunction electrode is rationally designed for both UOR and HER. The unique heterostructure facilitates electron transfer and interface interactions through local interfacial Co-Se/O-Fe bonding environment modulation, improving reaction kinetics and intrinsic activity. As a result, the heterostructured electrocatalyst exhibits ultralow potentials of −0.274 and 1.48 V to reach 500 mA cm⁻² for catalyzing the HER and UOR, respectively. Particularly, the full urea electrolysis system driven by Fe-Co_0.85Se/FeCo LDH delivers 300 mA cm⁻² at a relatively low potential of 1.57 V, which is 150 mV lower than the conventional water electrolysis. The combination of in situ characterization and theoretical analysis reveal that the active sites with the adjustable electronic environment are induced by the interfacial bonding of the heterojunction, facilitating the water decomposition of HER and the stabilization of intermediates in UOR. This work inspires the interfacial environment modulation to optimize advanced electrocatalysts for energy-saving H₂ production.     

Superb All-pH Hydrogen Evolution Performances Powered by Ultralow Pt-Decorated Hierarchical Ni-Mo Porous Microcolumns

Achieving efficient and robust hydrogen evolution reaction (HER) electrocatalysts under all-pH conditions is significant for clean hydrogen production. Herein, an ultralow Pt-decorated hierarchical Ni-Mo porous hybrid, consisting of Ni₃Mo₃N on MoO₂ microcolumns, is developed for all-pH HER with remarkable catalytic performances, owing to the porous structure, strong metal-support interaction, along with ultralow Pt nanoparticles and multichannel nickel foam support. The superhydrophilic and aerophilic surfaces favor mass transport during the HER process. Consequently, the porous Pt/Ni-Mo-N-O microcolumns present remarkable HER activity and durability with low overpotentials of 40.6, 101.1, and 89.5 mV to obtain 100 mA cm⁻² in basic, neutral, and acid media, respectively. Moreover, the excellent performance in alkaline seawater (40.4 mV@100 mA cm⁻²) even suppresses most of over-reported catalysts. More importantly, the two-electrode cell, assembled with Pt/Ni-Mo-N-O and NiMoO₄ as cathode and anode, exhibits excellent performance towards overall-water electrolysis with an ultralow cell voltage of 1.56 V@100 mA cm⁻².     

Graphdiyne Interface Engineering: Highly Active and Selective Ammonia Synthesis

A freestanding 3D graphdiyne–cobalt nitride (GDY/Co₂N) with a highly active and selective interface is fabricated for the electrochemical nitrogen reduction reaction (ECNRR). Density function theory calculations reveal that the interface‐bonded GDY contributes an unique p‐electronic character to optimally modify the Co‐N compound surface bonding, which generates as‐observed superior electronic activity for NRR catalysis at the interface region. Experimentally, at atmospheric pressure and room temperature, the electrocatalyst creates a new record of ammonia yield rate (Y ) and Faradaic efficiency (FE) of 219.72 μg h^?1 mg_cat.^?1 and 58.60 %, respectively, in acidic conditions, higher than reported electrocatalysts. Such a catalyst is promising to generate new concepts, new knowledge, and new phenomena in electrocatalytic research, driving rapid development in the field of electrocatalysis.     

CO在Pt及其合金表面电化学氧化和吸附的理论研究

文本综述了CO在Pt及其它过渡金属上电化学氧化机理的量子化学研究现状。系统论述了密度泛函理论计算在催化剂对CO电氧化的作用机制和CO与金属间吸附、成键及振动频率方面所给出的详细信息, 并指出了量子化学计算结果对于电极催化剂设计的指导意义。最后, 指出了目前量子化学计算的局限性并展望来其未来发展趋势。     

Synthesis of 3D IrRuMn Sphere as a Superior Oxygen Evolution Electrocatalyst in Acidic Environment

The design of a three-dimensional structure for an Ir-based catalyst offers a great opportunity to improve the electrocatalytic performance and maximize the use of the precious metal. Herein, a novel wet chemical strategy is reported for the synthesis of an IrRuMn catalyst with a sphere structure and porous features. In the synthetic process, the combined use of citric acid and formamide is requisite for the formation of the sphere structure. This method leads to a favorable 3D IrRuMn sphere structure with many fully exposed active sites. Furthermore, an alloying noble metal, such as Ir or Ru, with the transition metal leads to enhanced oxygen evolution reaction (OER) activity. The doping of a transition metal, such as Mn, is an interesting example, because it exhibits stability and activity in both acidic and alkaline media. For the OER, the IrRuMn sphere catalyst exhibits an overpotential of 260 mV at a current density of 10 mA cm⁻² in strongly acidic 0.1 m HClO₄, which is superior to that of a commercial IrO₂/C catalyst. This approach provides a novel way to synthesize an Ir-based multimetallic spherical electrocatalyst, which exhibits exceptional efficiency for the acidic OER. It will pave the way for new approaches to the practical utilization of PEM electrolyzers.