Water Oxidation Electrocatalyzed by an Efficient Mn₃O₄/CoSe₂ Nanocomposite

The design of efficient, cheap, and abundant oxygen evolution reaction (OER) catalysts is crucial to the development of sustainable energy sources for powering fuel cells. We describe here a novel Mn₃O₄/CoSe₂ hybrid which could be a promising candidate for such electrocatalysts. Possibly due to the synergetic chemical coupling effects between Mn₃O₄ and CoSe₂, the constructed hybrid displayed superior OER catalytic performance relative to its parent CoSe₂/DETA nanobelts. Notably, such earth-abundant cobalt (Co)-based catalyst afforded a current density of 10 mA cm^–2 at a small overpotential of ∼0.45 V and a small Tafel slope down to 49 mV/decade, comparable to the best performance of the well-investigated cobalt oxides. Moreover, this Mn₃O₄/CoSe₂ hybrid shows good stability in 0.1 M KOH electrolyte, which is highly required to a promising OER electrocatalyst

Surface Composition and Lattice Ordering-Controlled Activity and Durability of CuPt Electrocatalysts for Oxygen Reduction Reaction

We report the enhanced activity and stability of CuPt bimetallic tubular electrocatalysts through potential cycling in acidic electrolyte. A series of CuPt tubular electrocatalysts with sequential increased lattice ordering and surface atomic fraction of Pt were designed and synthesized by thermal annealing to reveal their improved electrocatalytic properties. These low-Pt-content electrocatalysts with Pt shell are formed through the thermal annealing and following potential cycling treatment. The catalysts (C1) with a low atomic fraction of Pt on the surface and low lattice ordering in the bulk are treated in acidic electrolyte, resulting in the formation of a Pt shell with relatively low activity and stability. However, the catalysts (C2) with a Pt-rich surface and high lattice ordering have a highly enhanced electrochemical surface area after potential cycling via surface roughing. The rough Pt shell of the C2 catalysts is achieved by leaching of surface Cu and the concomitant morphology restructuring. The C2 Pt surface demonstrated highly improved specific and mass activities of 0.8 mA cm_Pt^–2 and 0.232 A mg_Pt^–1 at 0.9 V for oxygen reduction reaction (ORR), and after 10 000 cycles, the C2 catalysts display almost no loss of the initial electrochemical active surface area (ECSA). Meanwhile, the stability of these CuPt catalysts shows regular change. Moreover, after a long-term stability measurement, the ECSA of C2 catalysts can be restored to the initial value after another potential cycling treatment, and thus, this kind of electrocatalyst may be developed as next-generation restorable cathode fuel cell catalysts

Quantifying the Nucleation and Growth Kinetics of Microwave Nanochemistry Enabled by in Situ High-Energy X‑ray Scattering

The fast reaction kinetics presented in the microwave synthesis of colloidal silver nanoparticles was quantitatively studied, for the first time, by integrating a microwave reactor with in situ X-ray diffraction at a high-energy synchrotron beamline. Comprehensive data analysis reveals two different types of reaction kinetics corresponding to the nucleation and growth of the Ag nanoparticles. The formation of seeds (nucleation) follows typical first-order reaction kinetics with activation energy of 20.34 kJ/mol, while the growth of seeds (growth) follows typical self-catalytic reaction kinetics. Varying the synthesis conditions indicates that the microwave colloidal chemistry is independent of concentration of surfactant. These discoveries reveal that the microwave synthesis of Ag nanoparticles proceeds with reaction kinetics significantly different from the synthesis present in conventional oil bath heating. The in situ X-ray diffraction technique reported in this work is promising to enable further understanding of crystalline nanomaterials formed through microwave synthesis

Nitrogen-Doped Graphene Supported CoSe₂ Nanobelt Composite Catalyst for Efficient Water Oxidation

The slow kinetics of the oxygen evolution reaction (OER) greatly hinders the large-scale production of hydrogen fuel from water splitting. Although many OER electrocatalysts have been developed to negotiate this difficult reaction, substantial progresses in the design of cheap, robust, and efficient catalysts are still required and have been considered a huge challenge. Here, we report a composite material consisting of CoSe₂ nanobelts anchored on nitrogen-doped reduced graphene oxides (denoted as NG-CoSe₂) as a highly efficient OER electrocatalyst. In 0.1 M KOH, the new NG-CoSe₂ catalyst afforded a current density of 10 mA cm^–2 at a small overpotential of mere 0.366 V and a small Tafel slope of ∼40 mV/decade, comparing favorably with the state-of-the-art RuO₂ catalyst. This NG-CoSe₂ catalyst also presents better stability than that of RuO₂ under harsh OER cycling conditions. Such good OER performance is comparable to the best literature results and the synergistic effect was found to boost the OER performance. These results raise the possibility for the development of effective and robust OER electrodes by using cheap and easily prepared NG-CoSe₂ to replace the expensive commercial catalysts such as RuO₂ and IrO₂

Investigation and Mitigation of Carbon Deposition over Copper Catalyst during Electrochemical CO₂ Reduction

Copper (Cu) is considered to be the most effective catalyst for electrochemical conversion of carbon dioxide (CO2) into value-added hydrocarbons, but its stability still faces considerable challenge. Here, we report the poisoning effect of carbon deposition during CO2 reduction on the active sites of Cu electrodea critical deactivation factor that is often overlooked. We find that, *C, an intermediate toward methane formation, could desorb on the electrode surface to form carbon species. We reveal a strong correlation between the formation of methane and the carbon deposition, and the reaction conditions favoring methane production result in more carbon deposition. The deposited carbon blocks the active sites and consequently causes rapid deterioration of the catalytic performance. We further demonstrate that the carbon deposition can be mitigated by increasing the roughness of the electrode and increasing the pH of the electrolyte. This work offers a new guidance for designing more stable catalysts for CO2 reduction