Graphene Quantum Dots-Supported Palladium Nanoparticles for Efficient Electrocatalytic Reduction of Oxygen in Alkaline Media

Abstract

Graphene quantum dots (GQDs)-supported palladium nanoparticles were synthesized by thermolytic reduction of PdCl 2 in 1,2propanediol at 80 °C in the presence of GQDs and then were subject to hydrothermal treatment at an elevated temperature within the range of 140 to 200 °C. Transmission electron microscopic measurements showed a raspberry-like morphology for the samples before and after hydrothermal treatment at temperatures ≤160 °C, where nanoparticles of ca. 8 nm in diameter formed large aggregates in the range of 50 to 100 nm in diameter, and at higher hydrothermal temperatures (180 and 200 °C), chain-like nanostructures were formed instead. X-ray photoelectron and Raman spectroscopic measurements revealed that the GQD structural defects were readily removed by hydrothermal treatments, and the defect concentrations exhibited a clear diminishment with increasing hydrothermal temperature, as indicated by the loss of oxygenated carbons in XPS and a drop in the D to G band ratio in Raman measurements. Voltammetric studies showed apparent electrocatalytic activity toward oxygen reduction, with a volcano-shaped variation of the activity with GQD defect concentration, and the peak activity was observed for the sample prepared at 180 °C with a mass activity of 23.9 A/g Pd and specific activity of 1.08 A/m 2 at +0.9 V vs RHE. This peak activity is attributed to optimal interactions between Pd and GQD where the GQD defects promoted charge transfer from metal to GQDs and hence weakened interactions with oxygenated intermediates, leading to enhanced ORR activity. The corresponding defect concentration was higher than that identified with the platinum counterparts due to the stronger affinity of oxygen to palladium.

Ultrasmall Palladium Nanoclusters Encapsulated in Porous Carbon Nanosheets for Oxygen Electroreduction in Alkaline Media

“…Meanwhile, the H 2 O 2 yield for Pd/CNS-20 % was < 10 % in the low overpotential range of 0 to + 0.80 V, close to that of Pd black. [25,34,43] Furthermore, the close Tafel slopes between the Pd/CNS series and Pd black suggests a similar reaction mechanism for ORR where the first electron reduction of oxygen was likely the rate determining step. The ORR kinetics may be further analyzed by using the KouteckyÀLevich (KÀL) Equation (3) [42] Figure 5e.…”

“…For example, Huang et al deposited Pd nanoparticles (average diameter 3 nm) on reduced graphene oxide and the composite exhibited a mass activity of only 88 A g À1 in 0.1 M KOH. [34] The much lower mass activity is probably due to the much larger Pd nanoparticles (~8 nm). [34] The much lower mass activity is probably due to the much larger Pd nanoparticles (~8 nm).…”

“…Recently, Zhao and coworkers prepared well defined thiolate-capped palladium clusters with the average molecular formula of Pd [13][14][15][16][17] (SR) [18][19][20][21][22] , and such clusters demonstrated apparent ORR activity and enhanced stability with or without ligand in alkaline solutions. [34][35] In another study, [36] Barman and coworkers prepared nanocomposites based on Pd nanoparticles-embedded porous graphitic carbon nitride which exhibited apparent ORR activity and robust stability. [33] Additionally, palladium clusters are prone to aggregation, dissolution, or decomposition during the electrocatalytic process.…”

The New Graphene Family Materials: Synthesis and Applications in Oxygen Reduction Reaction

“…The pioneering work of N-GQDs/graphene composites via the electrochemical approach for use as metal-free electrocatalysts for the ORR was reported by Qu et al [101]. As shown in Figure 5, the sizes of the as-prepared GQDs are about 2-5 nm (Figure 5a,b), and their heights are around 1-2.5 nm (Figure 5c), corresponding to 1-5 graphene layers.…”

A Roadmap for Achieving Sustainable Energy Conversion and Storage: Graphene-Based Composites Used Both as an Electrocatalyst for Oxygen Reduction Reactions and an Electrode Material for a Supercapacitor

“…Compared with Pt catalysts, these high cost-effective non-Pt catalysts that are mostly inclined to four-electron process would be better candidates for further industrial production if possible; while graphene-based composites dominate a large part among these catalytic species as well. Quite a few graphene and graphene-composite catalysts have been reported to provide an excellent activity and stability in alkaline conditions [17][18][19][20][21][22][23].…”