Anchored Pt-Co Nanoparticles on Honeycombed Graphene as Highly Durable Catalysts for the Oxygen Reduction Reaction

Abstract

Durability is an important factor in evaluating the performance of a catalyst. In this work, the spatial protection of the carrier to nanoparticles was considered to improve the durability of the catalyst. It is found that a honeycombed graphene with a three-dimensional (3D)-hierarchical porous structure (3D HPG) can help to reduce the shedding of Pt-Co nanoparticles (Pt-Co NPs) because 3D HPG can form a protective layer to reduce the direct erosion of Pt-Co NPs on the interface by an electrolyte. Then, appropriate oxygen groups were introduced on the 3D reduced hierarchical porous graphene oxide (3D rHPGO) to improve the dispersion of Pt-Co NPs on the surface of the carrier. It was found that the Pt d-band of the catalyst was anchored by π sites of carbonyl of an oxygen group. After optimization, the catalyst (referred to as Pt-Co/3D rHPGO) achieved a 2-fold enhancement in mass activity than that of a commercial Pt/C catalyst. More importantly, after the accelerated durability test (ADT) of 20 000 cycles, the Pt-Co/3D rHPGO catalyst can almost sustain this level of performance, whereas other catalysts showed a comparatively large loss of activity. According to the results, the high durability of Pt-Co/3D rHPGO was attributed to spatial protection of Pt-Co NPs and the defects on the surface allowed the electrolyte to enter. In addition, oxygen groups provided an anchoring effect on nanoparticles. Thus, the Pt-Co/3D rHPGO electrocatalyst exhibited splendid durability, holding a potential to be applied in PEMFC for long-term work.

Materials Research Directions Towards a Green Hydrogen Economy: A Review

“…The application of these materials is diverse, but the literature shows that the main interests are for the increase of surface area, porosity or just general improvements in morphology of Fuel Cell catalysts, especially for ORR. 232,234,236,238,239 This is further explored and demonstrated in the features of the most popular substances in hydrogen fuel cell research and their exemplary publications shown in Table 6. Many of the substances in Table 6 are comprised of the highlighted elements on Figure 13.…”

“…We suspect this is due to research efforts directed to the Oxygen Reduction Reaction (ORR), which occurs in the cathode of most fuel cells, being one of the major challenges when it comes to reducing cost. [231][232][233][234][235][236][237][238][239] One can also see the interest in tackling this challenge with other concepts, particularly "electrochemical reaction catalysts" and "electrochemical reduction" cluster. Similar to water splitting, the inclusion of concepts such as "nanoparticles" (also reflected on Table 1) and "Surface area" in this blue cluster confirms morphology and surface research as important parameters when optimizing catalysts.…”

Electrospun one-dimensional electrocatalysts for boosting electrocatalysis

“…55 Benefitting from these advantageous merits, these electrospun nanomaterials can thus work as promising electrocatalysts to largely promote the catalytic activity and efficiency. 56,57…”

Microwave Heating of Nanocrystals for Rapid, Low-Aggregation Intermetallic Phase Transformations

“…Intermetallic nanocrystals (NCs) are one of the most studied classes of materials for electrocatalysis − due to their high electrochemical stability − at lower precious metal loadings. ,,,− Pt–Co intermetallic face-centered-tetragonal (fct) phase (L1 0 ) NCs have been demonstrated as viable electrocatalysts for the oxygen reduction reaction (ORR). ,− The ability to perform the ORR with high electrochemical stability while decreasing the Pt loading is of key importance for proton exchange membrane fuel cells (PEMFCs), ,,− with the capability of providing a source of clean energy able to compete with fossil fuels . To make PEMFCs economically viable, there is a need to optimize the activity of the catalyst per unit Pt, , also known as the mass activity.…”

“…We use near-monodisperse Cu-doped PtCo 2 NCs in the intermetallic L1 0 phase as a model system. Copper-doping is known to reduce the barrier associated with the phase transformation. ,, The L1 0 phase is desirable because of simultaneously higher electrochemical stability and lower cobalt leaching during catalysis than the random alloy (A1) phase. − ,− ,,,, Typically, as-synthesized A1 face-centered-cubic (fcc) phase NCs are transformed into intermetallic L1 0 NCs by a thermal treatment that involves temperatures exceeding 400 °C over several hours. ,,,,, During this process, NC aggregation, or sintering, occurs, leading to a decrease in the electrochemically active surface area (ECSA) and resulting in a decrease in mass activity for the ORR. ,,, Several literature reports have attempted to prevent NCs from aggregating during the thermal treatment by anchoring the NCs to the substrate, ,, or by synthesizing the NCs directly in the intermetallic phase. ,,− Other methods have demonstrated a monodisperse dispersion of intermetallic NCs; however, these require a specialized technique such as Joule heating or electrochemical dealloying. ,− So far, no method has shown a complete phase transformation with minimized aggregation.…”