5 research outputs found
Water Oxidation Electrocatalyzed by an Efficient Mn<sub>3</sub>O<sub>4</sub>/CoSe<sub>2</sub> 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 Mn<sub>3</sub>O<sub>4</sub>/CoSe<sub>2</sub> hybrid which could be a promising
candidate for such electrocatalysts. Possibly due to the synergetic
chemical coupling effects between Mn<sub>3</sub>O<sub>4</sub> and
CoSe<sub>2</sub>, the constructed hybrid displayed superior OER catalytic
performance relative to its parent CoSe<sub>2</sub>/DETA nanobelts.
Notably, such earth-abundant cobalt (Co)-based catalyst afforded a
current density of 10 mA cm<sup>–2</sup> 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 Mn<sub>3</sub>O<sub>4</sub>/CoSe<sub>2</sub> 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<sub>Pt</sub><sup>–2</sup> and 0.232 A mg<sub>Pt</sub><sup>–1</sup> 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 CoSe<sub>2</sub> 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 CoSe<sub>2</sub> nanobelts anchored on nitrogen-doped reduced graphene oxides (denoted as NG-CoSe<sub>2</sub>) as a highly efficient OER electrocatalyst. In 0.1 M KOH, the new NG-CoSe<sub>2</sub> catalyst afforded a current density of 10 mA cm<sup>–2</sup> 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 RuO<sub>2</sub> catalyst. This NG-CoSe<sub>2</sub> catalyst also presents better stability than that of RuO<sub>2</sub> 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-CoSe<sub>2</sub> to replace the expensive commercial catalysts such as RuO<sub>2</sub> and IrO<sub>2</sub>
Investigation and Mitigation of Carbon Deposition over Copper Catalyst during Electrochemical CO<sub>2</sub> 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