Enhanced Formic Acid Oxidation over SnO₂-decorated Pd Nanocubes

Abstract

The formic acid oxidation reaction (FAOR) is one of the key reactions that can be used at the anode of low-temperature liquid fuel cells. To allow the knowledge-driven development of improved catalysts, it is necessary to deeply understand the fundamental aspects of the FAOR, which can be ideally achieved by investigating highly active model catalysts. Here, we studied SnO 2 -decorated Pd nanocubes (NCs) exhibiting excellent electrocatalytic performance for formic acid oxidation in acidic medium with a SnO 2 promotion that boosts the catalytic activity by a factor of 5.8, compared to pure Pd NCs, exhibiting values of 2.46 A mg –1 Pd for SnO 2 @Pd NCs versus 0.42 A mg –1 Pd for the Pd NCs and a 100 mV lower peak potential. By using ex situ, quasi in situ, and operando spectroscopic and microscopic methods (namely, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption fine-structure spectroscopy), we identified that the initially well-defined SnO 2 -decorated Pd nanocubes maintain their structure and composition throughout FAOR. In situ Fourier-transformed infrared spectroscopy revealed a weaker CO adsorption site in the case of the SnO 2 -decorated Pd NCs, compared to the monometallic Pd NCs, enabling a bifunctional reaction mechanism. Therein, SnO 2 provides oxygen species to the Pd surface at low overpotentials, promoting the oxidation of the poisoning CO intermediate and, thus, improving the catalytic performance of Pd. Our SnO x -decorated Pd nanocubes allowed deeper insight into the mechanism of FAOR and hold promise for possible applications in direct formic acid fuel cells.

Highly coordinated Pd overlayers on nanoporous gold for efficient formic acid electro-oxidation

“…S12 in the ESM). By normalizing the reduction charge of 420 μC•cm −2 for CO monolayer [6], the ECSAs of NPG-Pd1, NPG-Pd2, NPG-Pd3, and Pd/C were calculated to be 326.57, 196.96, 128.41, and 29.35 m 2 •g −1 , respectively. Meanwhile, CO tolerance of the catalysts can be evaluated via the potential of CO oxidation peak, because they reflect the additional potential required to overcome the activation energy of the reaction, and a smaller potential often means easier removal.…”

“…Regardless of the technical route adopted, the development of formic acid oxidation catalysts is very critical. It is well known that the electrochemical decomposition of formic acid follows two typical pathways [6,7], dehydrogenation (HCOOH → CO2 + H2) and dehydration (HCOOH → CO + H2O), where the latter path often leads to the catalyst poisoning due to strong adsorption of carbonaceous species on the catalyst surface such as Pt. Therefore, CO and OH adsorption energies (ΔECO and ΔEOH) are both recognized as appropriate descriptors to evaluate the formic acid oxidation reaction (FAOR) activity of an electrocatalyst [8,9].…”

Recent advances in electrocatalysts, mechanism, and cell architecture for direct formic acid fuel cells

“…(a) TEM image and elemental mapping of porous AgPt@Pt nano‐octahedra as well as comparison of FAEO electrocatalytic performance (activity and stability) of porous AgPt@Pt nano‐octahedra, Pt nano‐octahedra and commercial Pt black catalyst (Reprinted with permission (through Copyright Clearance Central) from reference (X. Jiang, Yan, et al, 2016) Copyright © 2016, American Chemical Society); (b) Scanning electron micrographs of titania nanotubes prepared by anodization process, and Pd dendrites deposited on titania nanotubes with inset showing higher magnification image (Reprinted with permission (through Copyright Clearance Central) from reference (B. G. Abraham et al, 2016) Copyright © 2016, WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim); (c) HAADF‐STEM image of Pd NCs and SnO 2 @Pd NCs with EDX mapping, as prepared and after cycling 10 times in formic acid (Reprinted with permission (through Copyright Clearance Central) from reference (Rettenmaier et al, 2020) Copyright © 2020, American Chemical Society); (d) STEM image of Pd‐ZrO 2 /MWCNTs (Reprinted with permission (through Copyright Clearance Central) from reference (Malolepszy et al, 2015) Copyright © 2015, Elsevier); (e) FE‐SEM micrographs of Pt/GC, Au/Pt/GC and MnO x /Au/Pt/GC electrodes and corresponding CVs in 0.3 M formic acid (Reprinted with permission (through Copyright Clearance Central) from reference (Mohammad et al, 2018) Copyright © 2017, Elsevier)…”

Benchmarking Catalysts for Formic Acid/Formate Electrooxidation

“…It is noteworthy that in the previously mentioned work with Pd a nanoparticles, Chen et al also explored the use of PdCuPt trimetallic alloy and t lyst has a similar onset potential as PdCu, 0.5 V vs. RHE, but the highest curren There is a plethora of publications using alloys based on Pd, the full scope of which is beyond this review [71,73,115,118,120,122,[124][125][126]128,129,133,134]. However, in a few exemplary studies, the maximum current, onset potential, propensity towards poisoning and stability can be improved when alloying Pd with metals such as Bi [124], Sn [135], Cd [124], In [125], Ag [71,115,118,[126][127][128], Cu [32,128,129,134], Ce [118], Co [118,133], Ni [118,120,126], Pt [39,71,73,91,92] and Au [129] (Table 3). For example, when comparing Pd black with PdCu nanoparticles, the onset potential is decreased from 0.8 to 0.5 V vs. RHE and the maximum current is increased from 27.3 to 84.6 mA cm −2 under identical, alkaline conditions [71].…”