Carbon Supported Noble Metal (Pd and Au) Catalysts Synthesized by an Oxide Route with High Performance for Oxygen Reduction in Acidic Mediaby José L. Fernández, Kasun P. Imaduwage, Cynthia G. Zoski

Electrochimica Acta

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Year
2015
DOI
10.1016/j.electacta.2015.08.027
Subject
Electrochemistry / Chemical Engineering (all)

Text

Electrochimica Acta 180 (2015) 460–470

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Electrochimica Acta j our na l ho me pa g e: www.elsev ier .com/ locate /e lec tac ta

Carbon Supported Noble Metal (Pd and Au) Catal an Oxid yge

Acidic

José L. Fe skia a Department o A b Programa de nivers a r t i c l

Article history:

Received 3 Jul

Received in re

Accepted 7 Au

Available onlin

Keywords:

Oxygen reduction

Metal oxide synthesis route

Electrocatalyst synergetic effects

Scanning electrochemical microscopy (SECM)

SECM activity d gol rtial died on pe strong effect of the reactant ratio (precursor salt/precipitant/reducing agent) on the performance of the resulting catalysts for oxygen reduction and hydrogen peroxide production. These SECM results were further confirmed using a rotating ring-disk electrode with Nafion-embedded Vulcan carbon supported dispersed metal nanoparticles, and characterization with XRD and TGA. A significant enhancement in the overall activity for the ORR was observed on both C/Pd and C/Au catalysts under conditions involving metal oxide reduction, compared to those catalysts that were synthesized by direct metal salt reduction.

For C/Pd, this enhanced overall activity with concomitant low peroxide yield is due to the different ways in 1. Introdu

The ove materials fo a number o degree of d ers [1]. Mec of a catalys onto an act via a 4-e− p tion of oxyg efficiency f diates that relative occ face proper ∗ Correspon

E-mail add (C.G. Zoski). 1 ISE memb http://dx.doi.o 0013-4686/© screening which the metal and unreduced metal oxide in the catalysts interact with the hydrogen peroxide pathway.

For C/Au, a highly dispersed metal with high electroactive area is obtained that shifts the potentials for the reduction of oxygen to hydrogen peroxide to near-reversible conditions. © 2015 Elsevier Ltd. All rights reserved. ction rall catalytic activity of dispersed carbon supported r the oxygen reduction reaction (ORR) is dependent on f factors that include nature of the catalyst, particle size, ispersion, and surface state of the catalyst, among othhanistic aspects that play key roles in the performance t for the ORR include the dissociative adsorption of O2 ive site, which is essential for the reaction to proceed athway, and the simultaneous electrochemical reducen to hydrogen peroxide, which decreases the faradaic or the 4-e-reduction to water and generates intermemay inhibit active sites for oxygen cleavage [2–8]. The urrence of these two processes is determined by the surties of the catalyst. Efficient electrocatalysts are those ding author. Tel.: +575-646-5292; fax: +575-646-2649. resses: jlfernan@fiq.unl.edu.ar (J.L. Fernández), czoski@nmsu.edu er. that reduce oxygen to water at the lowest overpotentials while concomitantly producing the least amount of H2O2. Overpotential is important in attaining high power densities in fuel cells [9], while peroxide yield is important from a practical point of view because H2O2 production leads to degradation of support materials as well as to the occurrence of corrosion processes, both of which ultimately contribute to a decrease in electrocatalytic efficiency [10].

The ORR continues to be the subject of significant research activity, especially in connection with discovering electrocatalysts that show better activity and which are less expensive and more abundant than Pt-based materials currently used in PEM fuel cells [11–15]. Despite more than a century of effort to identify effective

ORR electrocatalysts, the activation overpotential ranges from ≈ 0.3 to 0.45 V, even for Pt, resulting in cathode potentials that deviate significantly from the thermodynamic potential, Eo = 1.23 V vs NHE, in acidic solution. Catalyst formulations containing combinations of Pt and of other noble metals with less expensive metals continue to be investigated as possible replacements [16,17]. Pd and

Au are known to have very different behavior towards the reduction of molecular oxygen in acidic media. Pd is reported to catalyze rg/10.1016/j.electacta.2015.08.027 2015 Elsevier Ltd. All rights reserved.e Route with High Performance for Ox

Media rnándeza,b,1, Kasun P. Imaduwagea, Cynthia G. Zo f Chemistry and Biochemistry, New Mexico State University, Las Cruces, NM 88003, US

Electroquímica Aplicada e Ingeniería Electroquímica, Facultad de Ingeniería Química, U e i n f o y 2015 vised form 6 August 2015 gust 2015 e 12 August 2015 a b s t r a c t

Carbon supported palladium (C/Pd) an involving oxide precipitation and pa reaction (ORR) in acidic media was stu and tip-generation/substrate collectiysts Synthesized by n Reduction in ,∗ idad Nacional del Litoral, Santa Fe, Argentina d (C/Au) catalysts were synthesized through a synthesis route reduction, and their performance for the oxygen reduction . Scanning electrochemical microscopy (SECM) ORR screening rformed on glassy carbon supported metal spots showed a

J.L. Fernández et al. / Electrochimica Acta 180 (2015) 460–470 461 the 4e − reduction of oxygen to water [18], with the quantity of generated hydrogen peroxide determined by the surface state [19].

It is a noble metal with properties similar to and belonging to the same group of the periodic table as Pt, but is less active for the

ORR. Howev fifty times m demonstrat that of Pt [2 alloys and c procedures bination of to enhance of Pt [30–3 constituent oxygen red

In contr lower, and that of Pt a

Au oxidatio has the cap lic cathode (NPs), and activity [3,4 able on Au, intermediat product (i.e

In spite of t a good oxy lyst with e it has been cantly enha

ORR [52].

Here we the overall

Pd and Au itation/redu composed were prepa by chemica of oxide red for the OR alysts prep detected by

ORR activit (SECM) OR carbon (GC ferent degre preparation circular rea screened w color-coded compositio