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Substrate selection for fundamental studies of electrocatalysts and photoelectrodes: inert potential windows in acidic, neutral, and basic electrolyte.

Benck JD, Pinaud BA, Gorlin Y, Jaramillo TF - PLoS ONE (2014)

Bottom Line: In order to help researchers with the substrate selection process, we employ a consistent experimental methodology to evaluate the electrochemical reactivity and stability of seven potential substrate materials for electrocatalyst and photoelectrode evaluation.We determine the inert potential window for each substrate/electrolyte combination and make recommendations about which materials may be most suitable for application under different experimental conditions.Furthermore, the testing methodology provides a framework for other researchers to evaluate and report the baseline activity of other substrates of interest to the broader community.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical Engineering, Stanford University, Stanford, California, United States of America.

ABSTRACT
The selection of an appropriate substrate is an important initial step for many studies of electrochemically active materials. In order to help researchers with the substrate selection process, we employ a consistent experimental methodology to evaluate the electrochemical reactivity and stability of seven potential substrate materials for electrocatalyst and photoelectrode evaluation. Using cyclic voltammetry with a progressively increased scan range, we characterize three transparent conducting oxides (indium tin oxide, fluorine-doped tin oxide, and aluminum-doped zinc oxide) and four opaque conductors (gold, stainless steel 304, glassy carbon, and highly oriented pyrolytic graphite) in three different electrolytes (sulfuric acid, sodium acetate, and sodium hydroxide). We determine the inert potential window for each substrate/electrolyte combination and make recommendations about which materials may be most suitable for application under different experimental conditions. Furthermore, the testing methodology provides a framework for other researchers to evaluate and report the baseline activity of other substrates of interest to the broader community.

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Fluorine-doped tin oxide (FTO) substrate scanned over a single potential range and hydrogen evolution catalyzed by amorphous molybdenum sulfide on FTO.
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pone-0107942-g011: Fluorine-doped tin oxide (FTO) substrate scanned over a single potential range and hydrogen evolution catalyzed by amorphous molybdenum sulfide on FTO.

Mentions: Our progressive scan methodology offers unique advantages over the more common technique of sweeping over a single, arbitrary potential range. The latter method can underestimate the window of inertness. Take for example the case of FTO in 0.1 M H2SO4; our results show that the substrate remains inert to a cathodic potential of −0.39 V vs. RHE. However, sweeping over a wider range without progressively increasing the potential bound could lead to a baseline scan such as is shown in Figure 11 where instead the cathodic bound appears to be 0.01 V vs. RHE. The large oxidative and reductive features could lead a researcher to erroneously conclude that this substrate is unsuitable to study HER catalysts whereas it is in fact appropriate for moderately to highly active catalysts. As shown in Figure 11, the activity of an amorphous molybdenum sulfide HER catalyst can be measured accurately when using FTO as the substrate [87]. This catalyst reaches a current density of 10 mA/cm2 at approximately −0.2 V vs. RHE. This value is in excellent agreement with a previous study which showed the same overpotential when the catalyst was deposited on glassy carbon [87]. A second key advantage to progressive scanning is the ability to associate oxidative features with corresponding reductive features as they develop. Take now the case of a gold substrate in NaOH. The progressive scanning method revealed that feature c denoted in Figure 6 was reduction of accumulated oxygen on the surface. If a single scan had been employed, it may not have been readily apparent that this feature resulted from oxygen reduction, and instead it may have been attributed to the reduction of gold oxide or another process. The substrate may have therefore been deemed unsuitable for use at any potentials positive of 0.35 V vs. RHE due to the presence of these large reductive features. However, using the progressive scanning methodology, we observed that this reductive feature arose only after the positive potential bound was increased sufficiently to drive oxygen evolution, which provided strong evidence that feature c resulted from oxygen reduction. Our results using the progressive scanning methodology show that gold is an acceptable substrate up to a potential of 1.29 V vs. RHE in 0.1 M NaOH. In short, progressive scanning of the substrate gives a researcher significantly more information to facilitate accurate analysis of the electrochemical data pertaining to the supported electrocatalyst or photoelectrode.


Substrate selection for fundamental studies of electrocatalysts and photoelectrodes: inert potential windows in acidic, neutral, and basic electrolyte.

Benck JD, Pinaud BA, Gorlin Y, Jaramillo TF - PLoS ONE (2014)

Fluorine-doped tin oxide (FTO) substrate scanned over a single potential range and hydrogen evolution catalyzed by amorphous molybdenum sulfide on FTO.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4214636&req=5

pone-0107942-g011: Fluorine-doped tin oxide (FTO) substrate scanned over a single potential range and hydrogen evolution catalyzed by amorphous molybdenum sulfide on FTO.
Mentions: Our progressive scan methodology offers unique advantages over the more common technique of sweeping over a single, arbitrary potential range. The latter method can underestimate the window of inertness. Take for example the case of FTO in 0.1 M H2SO4; our results show that the substrate remains inert to a cathodic potential of −0.39 V vs. RHE. However, sweeping over a wider range without progressively increasing the potential bound could lead to a baseline scan such as is shown in Figure 11 where instead the cathodic bound appears to be 0.01 V vs. RHE. The large oxidative and reductive features could lead a researcher to erroneously conclude that this substrate is unsuitable to study HER catalysts whereas it is in fact appropriate for moderately to highly active catalysts. As shown in Figure 11, the activity of an amorphous molybdenum sulfide HER catalyst can be measured accurately when using FTO as the substrate [87]. This catalyst reaches a current density of 10 mA/cm2 at approximately −0.2 V vs. RHE. This value is in excellent agreement with a previous study which showed the same overpotential when the catalyst was deposited on glassy carbon [87]. A second key advantage to progressive scanning is the ability to associate oxidative features with corresponding reductive features as they develop. Take now the case of a gold substrate in NaOH. The progressive scanning method revealed that feature c denoted in Figure 6 was reduction of accumulated oxygen on the surface. If a single scan had been employed, it may not have been readily apparent that this feature resulted from oxygen reduction, and instead it may have been attributed to the reduction of gold oxide or another process. The substrate may have therefore been deemed unsuitable for use at any potentials positive of 0.35 V vs. RHE due to the presence of these large reductive features. However, using the progressive scanning methodology, we observed that this reductive feature arose only after the positive potential bound was increased sufficiently to drive oxygen evolution, which provided strong evidence that feature c resulted from oxygen reduction. Our results using the progressive scanning methodology show that gold is an acceptable substrate up to a potential of 1.29 V vs. RHE in 0.1 M NaOH. In short, progressive scanning of the substrate gives a researcher significantly more information to facilitate accurate analysis of the electrochemical data pertaining to the supported electrocatalyst or photoelectrode.

Bottom Line: In order to help researchers with the substrate selection process, we employ a consistent experimental methodology to evaluate the electrochemical reactivity and stability of seven potential substrate materials for electrocatalyst and photoelectrode evaluation.We determine the inert potential window for each substrate/electrolyte combination and make recommendations about which materials may be most suitable for application under different experimental conditions.Furthermore, the testing methodology provides a framework for other researchers to evaluate and report the baseline activity of other substrates of interest to the broader community.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical Engineering, Stanford University, Stanford, California, United States of America.

ABSTRACT
The selection of an appropriate substrate is an important initial step for many studies of electrochemically active materials. In order to help researchers with the substrate selection process, we employ a consistent experimental methodology to evaluate the electrochemical reactivity and stability of seven potential substrate materials for electrocatalyst and photoelectrode evaluation. Using cyclic voltammetry with a progressively increased scan range, we characterize three transparent conducting oxides (indium tin oxide, fluorine-doped tin oxide, and aluminum-doped zinc oxide) and four opaque conductors (gold, stainless steel 304, glassy carbon, and highly oriented pyrolytic graphite) in three different electrolytes (sulfuric acid, sodium acetate, and sodium hydroxide). We determine the inert potential window for each substrate/electrolyte combination and make recommendations about which materials may be most suitable for application under different experimental conditions. Furthermore, the testing methodology provides a framework for other researchers to evaluate and report the baseline activity of other substrates of interest to the broader community.

Show MeSH