Direct observation of the oxygenated species during oxygen reduction on a platinum fuel cell cathode

Casalongue, Hernan Sanchez; Kaya, Sarp; Viswanathan, Venkatasubramanian; Miller, David C.; Friebel, Daniel; Hansen, Heine Anton; Nørskov, Jens K.; Nilsson, Anders; Ogasawara, Hirohito

doi:10.1038/ncomms3817

Cited by 353 publications

(335 citation statements)

References 35 publications

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“…Other efforts are ongoing to increase the pressure limit and spatial resolution through changes in the cell/end station geometry and lenses, with large strides being made at synchrotrons around the world to reach close to atmospheric pressures. [62][63] An additional approach includes the use of X-ray lenses to produce standing waves, increasing the depth resolution of sample/interface analysis. 61,64 Finally, novel pump-probe techniques using AP-XPS coupled to laser systems (and the free-electron laser) can also provide unique time-resolved information.…”

Section: Discussionmentioning

confidence: 99%

Insights into Electrochemical Reactions from Ambient Pressure Photoelectron Spectroscopy

et al. 2015

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ConspectusThe understanding of fundamental processes in the bulk and at the interfaces of electrochemical devices is a prerequisite for the development of new technologies with higher efficiency and improved performance. One energy storage scheme of great interest is splitting water to form hydrogen and oxygen gas, and converting back to electrical energy by their subsequent recombination with only water as a by-product. However, kinetic limitations to the rate of oxygen-based electrochemical reactions hamper the efficiency in technologies such as solar fuels, fuel cells, and electrolyzers. For these reactions, the use of metal oxides as electrocatalysts is prevalent due to their stability, low cost, and ability to store oxygen within the lattice. However, due to the inherently convoluted nature of electrochemical and chemical processes in electrochemical systems, it is difficult to isolate and study individual electrochemical processes in a complex system. Therefore in situ characterization tools are required for observing related physical and chemical processes directly at the places where and while they occur, and can help elucidate the mechanisms of charge separation and charge transfer at electrochemical interfaces.X-ray photoelectron spectroscopy (XPS), also known as ESCA (electron spectroscopy for chemical analysis) has been used as a quantitative spectroscopic technique that measures the elemental composition, as well as chemical and electronic state of a material. Building from extensive ex situ characterization of electrochemical systems, initial in situ studies were conducted at (near) UHV conditions (≤10 −6 Torr) to probe solid-state electrochemical systems. However through the integration of differential-pumping stages, XPS can now operate at pressures in the Torr range, comprising a technique called ambient pressure XPS (AP-XPS).In this Account, we briefly review the working principles and current status of AP-XPS. We use several recent in situ studies on model electrochemical components as well as operando studies performed by our groups at the Advanced Light Source (ALS) at Lawrence Berkeley National Lab to illustrate that AP-XPS is both a chemically and electrically specific tool since photoelectrons carry information on both the local chemistry and electrical potentials. The applications of AP-XPS to oxygen electrocatalysis shown in this Account span well defined studies of (1) the oxide/oxygen gas interface, (2) the oxide/water vapor interface, and (3) operando measurements of half and full electrochemical cells. Using 2 specially designed model devices, we can expose and isolate the electrode or interface of interest to the incident X-ray beam and AP-XPS analyzer to relate the electrical potentials to the composition/chemical state of the key components and interfaces. We conclude with an outlook on new developments of AP-XPS endstations, which may provide significant improvement in the observation of dynamics over a wide range of time scale, higher spatial resolution, and improved characteri...

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Section: Discussionmentioning

confidence: 99%

Insights into Electrochemical Reactions from Ambient Pressure Photoelectron Spectroscopy

et al. 2015

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“…To further complement the electronic structure information that was obtained by probing Fe and Ni sites with XAS, we employ here X-ray photoemission spectroscopy (XPS), which can directly probe the chemical state of hydroxide/oxide ligands and species in the electrolytic double layer. The limitation of XPS to vacuum conditions 7 has been overcome with the recent development of ambient pressure X-ray photoelectron spectroscopy (APXPS) and third generation synchrotron radiation sources that have enabled XPS analysis under electrochemical reaction conditions of solid-gas interfaces in solid-state electrochemical cells, 8,9 at the triple-phase boundary between gas phase, electrolyte and electrocatalyst in proton exchange membrane fuel cells and electrolyzers, [9][10][11] and at the solidliquid interface in three-electrode electrochemical cells. [12][13][14] The latter approach is used here to study a Ni-Fe electrocatalyst for water splitting.…”

Section: Introductionmentioning

confidence: 99%

Ambient-Pressure XPS Study of a Ni–Fe Electrocatalyst for the Oxygen Evolution Reaction

et al. 2016

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Chemical analysis of solid-liquid interfaces under electrochemical conditions has recently become feasible due to the development of new synchrotron radiation techniques. Here we report the use of "tender" X-ray Ambient Pressure X-ray Photoelectron Spectroscopy (APXPS) to characterize a thin film of Ni-Fe oxyhydroxide electrodeposited on Au as the working electrode at different applied potentials in 0.1 M KOH as the electrolyte. Our results show that the asprepared 7 nm thick Ni-Fe (50% Fe) film contains Fe and Ni in both their metallic as well as oxidized states, and undergoes further oxidation when the sample is subjected to electrochemical oxidation-reduction cycles. Metallic Fe is oxidized to Fe 3+ and metallic Ni to Ni 2+/3+ . This work shows that it is possible to monitor the chemical nature of the Ni-Fe catalyst as function of potential when the corresponding current densities are small. This allows for operando measurements just above the onset of OER; however, current densities as they are desired in photoelectrochemical devices (~1-10 mA cm -2 ) could not be achieved in this work, due to ohmic losses in the thin electrolyte film. We use a two-dimensional model to describe-the spatial distribution of the electrochemical potential, current density and pH as a function of the position above the electrolyte meniscus, to provide guidance towards enabling the acquisition of operando APXPS at high current density. The shifts in binding energy of water with applied potential predicted by the model is in good agreement with the experimental values.3

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“…11 As shown in Table I, each catalyst incorporated in the MEA had a different initial average Co content, e.g., 34,20, and 15 mol%, as measured in the cathode catalyst layer (CCL), for catalysts H, M, and L, respectively. Catalysts H and M were supplied as powders.…”

mentioning

confidence: 99%

Durability of Pt-Co Alloy Polymer Electrolyte Fuel Cell Cathode Catalysts under Accelerated Stress Tests

Papadias

Ahluwalia

Kariuki

et al. 2018

J. Electrochem. Soc.

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The durability of Pt-Co alloy cathode catalysts supported on high surface area carbon is investigated by subjecting them to accelerated stress tests (ASTs). The catalysts had different initial Co contents and nanoparticle morphologies: a "spongy" porous morphology for the high-Co (H) content catalyst, and a fully alloyed crystalline morphology for the medium-Co (M) and low-Co (L) content catalysts. The specific activity of the catalysts depends on their initial Co content, morphology and nanoparticle size, and remained higher than 1000 μA/cm 2 -Pt after 27-50% Co loss. The H-catalyst electrode showed the smallest kinetic overpotentials (η c s ) due to higher initial Pt loading than the other two electrodes, but it had the fastest increase in η c s with AST cycling due to lower Co retention; the L-catalyst electrode showed higher η c s due to a lower initial Pt loading, but had a smaller increase in η c s with aging due to higher Co retention; the M-catalyst electrode showed a similar increase in η c s with aging, but this increase was due to the combined effects of Co dissolution and electrochemically active surface area (ECSA) loss. The modeled increase in mass transfer overpotentials with aging correlates with the initial Pt loading, ECSA loss and the initial catalyst morphology.

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Direct observation of the oxygenated species during oxygen reduction on a platinum fuel cell cathode

Cited by 353 publications

References 35 publications

Insights into Electrochemical Reactions from Ambient Pressure Photoelectron Spectroscopy

Insights into Electrochemical Reactions from Ambient Pressure Photoelectron Spectroscopy

Ambient-Pressure XPS Study of a Ni–Fe Electrocatalyst for the Oxygen Evolution Reaction

Durability of Pt-Co Alloy Polymer Electrolyte Fuel Cell Cathode Catalysts under Accelerated Stress Tests

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