High Throughput Thin Film Pt-M Alloys for Fuel Electrooxidation: Low Concentrations of M (M = Sn, Ta, W, Mo, Ru, Fe, In, Pd, Hf, Zn, Zr, Nb, Sc, Ni, Ti, V, Cr, Rh)

Abstract

Eighteen Pt-M binary (M = Sn, Ta, W, Mo, Ru, Fe, In, Pd, Hf, Zn, Zr, Nb, Sc, Ni, Ti, V, Cr, Rh) thin film composition spreads were deposited at low M concentrations using magnetron sputtering and screened for methanol and ethanol electrooxidation activity using a fluorescence assay. Characterization of these thin films was performed using high energy X-ray diffraction and X-ray fluorescence. The electrochemical fluorescence assay revealed highest activity in the films with M = Sn, Zn, In, Fe, and Ru. Pt-M (M = Sn, Zn, In) showed highest activity at concentrations below 5 atom-% with a high fraction of Pt fcc(111) texturing and Pt-Fe showing the best activity at 10 atom-% Fe. On the other hand, the best (most negative) fluorescence onset potential in the Pt-Ru system was observed at a concentration of 35 atom-% Ru with only slight texturing of the film. To explore the potential origins of the observed catalytic activity, preliminary calculations on the d-band center shift with alloying were performed for bulk concentrations of up to 30 atom-% for Fe and 16 atom-% for M = Sn, Zn.Fuel cells present a promising energy conversion technology that is not limited by the Carnot cycle efficiency. Fuel cell efficiencies can reach up to 80-90% whereas a typical Carnot engine can only reach a maximum efficiency of 45-50%. 1 Fuel cells, in principle, could provide higher efficiency, an environmentally friendly form of energy conversion and high power/energy density. While the ideal system is a hydrogen-oxygen proton exchange membrane fuel cell (PEMFC), transportation, storage, and widespread availability of hydrogen is challenging due to the required high pressures and low volumetric energy density when compared to other fuels. Methanol, ethanol, and other small organic molecules (SOMs) have the advantage of higher volumetric energy densities, easier transportation, and diversity of availability from biosources. 2 Present limitations for widespread deployment of fuel cells are the cathode and anode materials which are expensive, easily poisoned, and show degradation over time. For methanol and ethanol oxidation, the process is more complicated than in the case of hydrogen, since the carbon in the fuel must be oxidized to CO 2 for maximal efficiency. The catalyst must also exhibit high catalytic activity for fuel oxidation with minimal poisoning. Platinum is the most commonly used catalyst, but it is readily poisoned with even low (ppm) levels of CO. As CO stands as a general and ubiquitous intermediate in the oxidation of SOMs, different catalysts must be used/found. Many materials have been investigated as anode catalysts for the oxidation of methanol, ethanol, and ethylene glycol, including alloys, 3 intermetallics, 4 nonPt containing materials (carbides, nitrides, oxides), 5 and core-shell structures. 6 For the cathode case, Strasser et al. reported improved activity for oxygen reduction with a Pt shell and a Pt-Cu alloyed core when compared to Pt alone. 6a They also considered the improved activity to be a result of the...

Combinatorial PtSnM (M = Fe, Ni, Ru and Pd) nanoparticle catalyst library toward ethanol electrooxidation

“…The nanoparticle combinatorial library was constructed as described in [31]. -----------------------Figure 1 -----------------------The fluorescence assay described in [33] was employed to assess the catalytic properties of the Pt-based catalysts. A Teflon electrochemical cell was sealed with an oring atop a 3-inch diameter catalyst array.…”

“…Tague et al [33] studied combinatorial libraries of Pt-M alloy (M = a wide variety (18 different) of metals) thin films for methanol and ethanol electroxidation. Films were prepared using a combinatorial sputter deposition system and screened by a fluorescence assay.…”

CRYSTAL: a multi-agent AI system for automated mapping of materials’ crystal structures

“…AgCl. [30] The Pd 0.17 Rh 0.33 Ta 0.5 catalyst is the only known Pt-free catalyst with onset potential in this range. The onset potential of 0.5 V versus RHE is also within the range of onset overpotentials observed with Pd-based catalyst in alkaline electrolytes, [22] and given the inactivity of Pd and Rh in the weak acidic electrolyte used in our experiments, the Ta-based intermetallics appear to enable the activity at lower pH, opening a new direction for catalyst development and a pathway for the further development of Pt-free catalysts.…”

Addition of iron oxide to Pt-based catalyst to enhance the catalytic activity of ethanol electrooxidation

“…Iron and iron oxide have recently gained attention because they can be used as co-catalyst or conductive support during the oxidation of alcohols. Few researchers have employed these materials to oxidize methanol [50][51][52][53], ethanol [54][55][56][57], or glycerol [58]. Iron and Fe 2 O 3 are advantageous co-catalysts or supports for Pt-based catalysts: they are inexpensive as compared to other metal oxides, and they present excellent physicochemical properties, such as high surface, porosity, and electropositivity, which enhances the activity of Ptbased catalysts and contributes to the occurrence of electronic and bifunctional mechanism over Pt.…”