Abstract
Formic acid (FA) electro-oxidation (FAO) was investigated at a binary catalyst composed of palladium nanoparticles (PdNPs) and copper oxide nanowires (CuOxNWs) and assembled onto a glassy carbon (GC) electrode. The deposition sequence of PdNPs and CuOxNWs was properly adjusted in such a way that could improve the electrocatalytic activity and stability of the electrode toward FAO. Several techniques including cyclic voltammetry, chronoamperometry, field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction were all combined to report the catalyst’s activity and to evaluate its morphology, composition, and structure. The highest catalytic activity and stability were obtained at the CuOx/Pd/GC electrode (with PdNPs directly deposited onto the GC electrode followed by CuOxNWs with a surface coverage,Г, of ca. 49%). Such enhancement was inferred from the increase in the peak current of direct FAO (by ca. 1.5 fold) which associated a favorable negative shift in its onset potential (by ca. 30 mV). The enhanced electrocatalytic activity and stability (decreasing the loss of active material by ca. 1.5-fold) of the CuOx/Pd/GC electrode was believed originating both from facilitating the direct oxidation (decreasing the time needed to oxidize a complete monolayer of FA, increasing turnover frequency, by ca. 2.5-fold) and minimizing the poisoning impact (by ca. 71.5%) at the electrode surface during FAO.
Highlights
Formic acid (FA) electro-oxidation (FAO) was investigated at a binary catalyst composed of palladium nanoparticles (PdNPs) and copper oxide nanowires (CuOxNWs) and assembled onto a glassy carbon (GC) electrode. e deposition sequence of PdNPs and CuOxNWs was properly adjusted in such a way that could improve the electrocatalytic activity and stability of the electrode toward FAO
Such enhancement was inferred from the increase in the peak current of direct FAO which associated a favorable negative shift in its onset potential. e enhanced electrocatalytic activity and stability of the CuOx/Pd/GC electrode was believed originating both from facilitating the direct oxidation and minimizing the poisoning impact at the electrode surface during FAO
For the CuOx/GC electrode (Figure 1(b)), a main oxidation peak appeared at ca. 0.15 V coupled with a reduction peak after ca. 0 V corresponding to the CuOx formation and reduction [27, 29]
Summary
E deposition sequence of PdNPs and CuOxNWs was properly adjusted in such a way that could improve the electrocatalytic activity and stability of the electrode toward FAO. E catalytic performance of Pd catalysts toward FAO was recently enhanced by doping with other metals and/or metal oxides that have the capacity to reduce the adsorption of these poisoning intermediates [31,32,33,34]. Modified electrodes toward FAO was examined in an aqueous solution of 0.3 M FA solution (pH 3.5, pH was adjusted by adding a proper amount of NaOH) at a scan rate of 100 mV·s−1 (first cycle is recorded) At this pH, the polarization resistance will be reduced, the solution ionic conductivity was enhanced [39]. An X-ray diffraction (XRD, PANalytical, X’Pert PRO) operated with Cu target (λ 1.54 A ) revealed the crystallographic structure of the modified catalysts. e inductively coupled plasma optical emission spectrometry, ICP-OES, (Perkin Elmer, Optima 8000) has been utilized to specify if there was a loss in the catalysts’ materials (Pd&Cu) after the prolonged electrolysis and to determine the amounts lost
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