Electrocatalysts Prepared by Galvanic Replacement

Abstract

Galvanic replacement is the spontaneous replacement of surface layers of a metal, M, by a more noble metal, M noble , when the former is treated with a solution containing the latter in ionic form, according to the general replacement reaction: nM + mM noble n+ → nM m+ + mM noble. The reaction is driven by the difference in the equilibrium potential of the two metal/metal ion redox couples and, to avoid parasitic cathodic processes such as oxygen reduction and (in some cases) hydrogen evolution too, both oxygen levels and the pH must be optimized. The resulting bimetallic material can in principle have a M noble-rich shell and M-rich core (denoted as M noble (M)) leading to a possible decrease in noble metal loading and the modification of its properties by the underlying metal M. This paper reviews a number of bimetallic or ternary electrocatalytic materials prepared by galvanic replacement for fuel cell, electrolysis and electrosynthesis reactions. These include oxygen reduction, methanol, formic acid and ethanol oxidation, hydrogen evolution and oxidation, oxygen evolution, borohydride oxidation, and halide reduction. Methods for depositing the precursor metal M on the support material (electrodeposition, electroless deposition, photodeposition) as well as the various options for the support are also reviewed. 1. Principle of Galvanic Replacement/Deposition 1.1. Thermodynamic Considerations When a metal, M (e.g., Cu, Fe, Co, Ni, Al, etc.), is immersed in a solution containing ions of a more noble metal, M noble n+ (e.g., Pt, Au, Pd, Ag, Ru, Ir, Rh, Os, etc.-i.e., a metal with a higher standard potential) then, due to the difference in their standard electrochemical potentials, E 0 noble − E 0 > 0, and provided that the ionic form of M is stable under the given experimental conditions (of temperatue, pH, complexing agents etc.), the following reaction is thermodynamically favored and can take place spontaneously: M noble n+ + n/m M → M noble + n/m M m+ (1) This reaction, which bears similarities with transmetalation reactions between metal complexes [1] and is also known as immersion plating [2] in the plating industry and galvanic replacement [3] in materials chemistry, can be considered to originate from the coupling of the following two half-reactions: M noble n+ + ne − ↔ M noble (E 0 noble) (2) M m+ + me − ↔ M (E 0) (3)

On‐the‐fly Catalyst Modification: Strategy to Improve Catalytic Processes Selectivity and Understanding

“…On‐the‐fly modification entails modification of catalyst metal surface by dopant(s) followed by the catalytic reaction that quantifies the effect of the modification. Nevertheless, we think methods such as atomic layer deposition (ALD), controlled surface reactions (CSR), and galvanic displacement can be easily adapted to performed similar on‐the‐fly modifications.…”

Core–Shell Pd@M (M=Ni, Cu, Co) Nanoparticles/Graphene Ensembles with High Mass Electrocatalytic Activity Toward the Oxygen Reduction Reaction

“…[19] The successful replacement was confirmed and quantified by measuring the UV/Vis absorption of the released M 2 + speciesi nt he supernatant solutiona fter the Pd@M NPs synthesis ( Figure S1 in the Supporting Information). [19] The successful replacement was confirmed and quantified by measuring the UV/Vis absorption of the released M 2 + speciesi nt he supernatant solutiona fter the Pd@M NPs synthesis ( Figure S1 in the Supporting Information).…”

“…This is at hermodynamically favorable reactiona st he standard potentials of the Ni 2 + /Ni, Cu 2 + /Cu, and Co 2 + /Co couples are À0.257, À0.277, and + 0.340 V( vs. standard hydrogen electrode, SHE), respectively,l ower than that of PdCl 4 2À /Pd, being + 0.620 V( vs. SHE). [19] The successful replacement was confirmed and quantified by measuring the UV/Vis absorption of the released M 2 + speciesi nt he supernatant solutiona fter the Pd@M NPs synthesis ( Figure S1 in the Supporting Information). Based on these data, the Pd-to-M( M= Ni, Cu, Co) mass ratios were calculatedt ob e2 8:72, 30:70, and 29:71f or Pd@Ni NPs , Pd@Cu NPs ,a nd Pd@Co NPs ,r espectively,w hich are very close to the theoretically expected, asd esigned, value of 30:70.…”

Electrodeposition of two-dimensional Pt nanostructures on highly oriented pyrolytic graphite (HOPG): the effect of evolved hydrogen and chloride ions

“…In particular, Pt extended surfaces deposited on high aspect-ratio materials such as nanofibers [19,21] and whiskers [22] presented exceptional increase of the ORR specific activity, which was kept after prolonged electrochemical cycling. Among the methods being investigated to produce Pt conformal thin films, atomic layer deposition (ALD), electrochemical atomic layer deposition (EC-ALD), pulsed laser deposition, surface-limited redox replacement (SLRR), galvanic displacement [18,[23][24][25] and other vacuum techniques, such as magnetron sputtering are employed [26].…”