15 research outputs found
Domain Structures of Ni and NiFe (Oxy)Hydroxide Oxygen-Evolution Catalysts from Xâray Pair Distribution Function Analysis
NiâFe
(oxy)Âhydroxides, Ni<sub>(1â<i>z</i>)</sub>Fe<sub><i>z</i></sub>O<sub><i>x</i></sub>H<sub><i>y</i></sub>, are among the fastest-known water
oxidation catalysts in alkaline media on a per-cation basis. At current
densities relevant for electrolysis (e.g., >0.5 A/cm<sup>â2</sup>), mass and electron transport through catalyst films with high mass
loading are critical and depend substantially on the extended and
intermediate catalyst architecture. Here we use X-ray pair distribution
function (PDF) analysis to determine the intermediate nanostructures
of electrodeposited Ni<sub>(1â<i>z</i>)</sub>Fe<sub><i>z</i></sub>O<sub><i>x</i></sub>H<sub><i>y</i></sub> films. We report the effects of electrodeposition
technique (pulsed versus continuous), electrochemical cycling, and
Fe content on the structure of the catalyst film. The PDF patterns
for Ni<sub>(1â<i>z</i>)</sub>Fe<sub><i>z</i></sub>O<sub><i>x</i></sub>H<sub><i>y</i></sub> films are best simulated by model structures consisting of brucite-like
ÎČ-NiÂ(OH)<sub>2</sub> fragments 1 to 3 layers in thickness. Only
the oxidation state of the film significantly affects the intralayer
scattering behavior (i.e., metalâoxygen bond distance). The
interlayer interactions, however, are affected by Fe content and deposition
conditions. The domain size of many of the systems are similar, extending
to âŒ5 nm, which are best modeled by sheets containing upward
of âŒ250 metal cations. Smaller domains were found for films
deposited through a larger number of electrochemical cathodic current
pulses. Films can be cycled between as-deposited, oxidized, and reduced
states, with minimal loss of intrasheet coherence, indicating a degree
of structural stability. We estimate heterogeneity in the domain structures
by modeling the PDF data to linear combinations of oxyhydroxide fragments
with different sizes and numbers of layers
Advanced and In Situ Analytical Methods for Solar Fuel Materials.
In situ and operando techniques can play important roles in the development of better performing photoelectrodes, photocatalysts, and electrocatalysts by helping to elucidate crucial intermediates and mechanistic steps. The development of high throughput screening methods has also accelerated the evaluation of relevant photoelectrochemical and electrochemical properties for new solar fuel materials. In this chapter, several in situ and high throughput characterization tools are discussed in detail along with their impact on our understanding of solar fuel materials
Advanced and In Situ Analytical Methods for Solar Fuel Materials
In situ and operando techniques can play important roles in the development of better performing photoelectrodes, photocatalysts, and electrocatalysts by helping to elucidate crucial intermediates and mechanistic steps. The development of high throughput screening methods has also accelerated the evaluation of relevant photoelectrochemical and electrochemical properties for new solar fuel materials. In this chapter, several in situ and high throughput characterization tools are discussed in detail along with their impact on our understanding of solar fuel materials