79 research outputs found
Effects of Gold Substrates on the Intrinsic and Extrinsic Activity of High-Loading Nickel-Based Oxyhydroxide Oxygen Evolution Catalysts
We systematically investigate the
effects of Au substrates on the
oxygen evolution activities of cathodically electrodeposited nickel
oxyhydroxide (NiOOH), nickel–iron oxyhydroxide (NiFeOOH), and
nickel–cerium oxyhydroxide (NiCeOOH) at varying loadings from
0 to 2000 nmol of metal/cm<sup>2</sup>. We determine that the geometric
current densities, especially at higher loadings, were greatly enhanced
on Au substrates: NiCeOOH/Au reached 10 mA/cm<sup>2</sup> at 259 mV
overpotential, and NiFeOOH/Au achieved 140 mA/cm<sup>2</sup> at 300
mV overpotential, which were much greater than those of the analogous
catalysts on graphitic carbon (GC) substrates. By performing a loading
quantification using both inductively coupled plasma optical emission
spectrometry and integration of the Ni<sup>2+/3+</sup> redox peak,
we show that the enhanced activity is predominantly caused by the
stronger physical adhesion of catalysts on Au. Further characterizations
using impedance spectroscopy and <i>in situ</i> X-ray absorption
spectroscopy revealed that the catalysts on Au exhibited lower film
resistances and higher number of electrochemically active metal sites.
We attribute this enhanced activity to a more homogeneous electrodeposition
on Au, yielding catalyst films with very high geometric current densities
on flat substrates. By investigating the mass and site specific activities
as a function of loading, we bridge the practical geometric activity
to the fundamental intrinsic activity
Transition Metal Arsenide Catalysts for the Hydrogen Evolution Reaction
We report, to our knowledge for the first time, a combined experimental and density functional theory (DFT) investigation into the activity and stability of cobalt, molybdenum, and copper arsenides as catalysts for the hydrogen evolution reaction (HER). We find CoAs and MoAs to be the most active arsenide materials. We discuss the trends between calculated surface vacancy formation energies and catalyst stability. Using a simple thermodynamic model of HER activity, we find consistent trends between hydrogen binding free energy and the experimentally observed activity
The Predominance of Hydrogen Evolution on Transition Metal Sulfides and Phosphides under CO_2 Reduction Conditions: An Experimental and Theoretical Study
A combination of experiment and theory has been used to understand the relationship between the hydrogen evolution reaction (HER) and CO_2 reduction (CO_2R) on transition metal phosphide and transition metal sulfide catalysts. Although multifunctional active sites in these materials could potentially improve their CO_2R activity relative to pure transition metal electrocatalysts, under aqueous testing conditions, these materials showed a high selectivity for the HER relative to CO_2R. Computational results supported these findings, indicating that a limitation of the metal phosphide catalysts is that the HER is favored thermodynamically over CO_2R. On Ni-MoS_2, a limitation is the kinetic barrier for the proton–electron transfer to *CO. These theoretical and experimental results demonstrate that selective CO_2R requires electrocatalysts that possess both favorable thermodynamic pathways and surmountable kinetic barriers
The Predominance of Hydrogen Evolution on Transition Metal Sulfides and Phosphides under CO<sub>2</sub> Reduction Conditions: An Experimental and Theoretical Study
A combination
of experiment and theory has been used to understand
the relationship between the hydrogen evolution reaction (HER) and
CO<sub>2</sub> reduction (CO<sub>2</sub>R) on transition metal phosphide
and transition metal sulfide catalysts. Although multifunctional active
sites in these materials could potentially improve their CO<sub>2</sub>R activity relative to pure transition metal electrocatalysts, under
aqueous testing conditions, these materials showed a high selectivity
for the HER relative to CO<sub>2</sub>R. Computational results supported
these findings, indicating that a limitation of the metal phosphide
catalysts is that the HER is favored thermodynamically over CO<sub>2</sub>R. On Ni-MoS<sub>2</sub>, a limitation is the kinetic barrier
for the proton–electron transfer to *CO. These theoretical
and experimental results demonstrate that selective CO<sub>2</sub>R requires electrocatalysts that possess both favorable thermodynamic
pathways and surmountable kinetic barriers
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