Structure/Processing/Properties Relationships in Nanoporous Nanoparticles As Applied to Catalysis of the Cathodic Oxygen Reduction Reaction

Abstract

We present a comprehensive experimental study of the formation and activity of dealloyed nanoporous Ni/Pt alloy nanoparticles for the cathodic oxygen reduction reaction. By addressing the kinetics of nucleation during solvothermal synthesis we developed a method to control the size and composition of Ni/Pt alloy nanoparticles over a broad range while maintaining an adequate size distribution. Electrochemical dealloying of these size-controlled nanoparticles was used to explore conditions in which hierarchical nanoporosity within nanoparticles can evolve. Our results show that in order to evolve fully formed porosity, particles must have a minimum diameter of ∼15 nm, a result consistent with the surface kinetic processes occurring during dealloying. Nanoporous nanoparticles possess ligaments and voids with diameters of approximately 2 nm, high surface area/mass ratios usually associated with much smaller particles, and a composition consistent with a Pt-skeleton covering a Ni/Pt alloy core. Electrochemical measurements show that the mass activity for the oxygen reduction reaction using carbon-supported nanoporous Ni/Pt nanoparticles is nearly four times that of commercial Pt/C catalyst and even exceeds that of comparable nonporous Pt-skeleton Ni/Pt alloy nanoparticles.

Electrochemical Synthesis of Ammonia: A Low Pressure, Low Temperature Approach

“…There is evidence elsewhere in the field of electrochemical catalysis that nanostructured materials result in performance and selectivity enhancements, most notably in the large and growing bodies of literature focused on the development of low-poisoning, high-activity oxygen reduction reaction catalysts and catalysts for methanol electrooxidation. [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] Lessons learned thus far from theory and experiment point towards the potential successful use of non-precious metals in multi-metallic nanostructured materials for enhanced electrocatalytic performance.…”

Electrochemical preparation and characterization of PdPt nanocages with improved electrocatalytic activity toward oxygen reduction reaction

“…On the other hand, the shape and morphology of nanocrystals are also of great importance in the development of ORR catalysts. Therein, porous nanocatalysts [9][10][11][12][13][14][15][16] are attracting more and more attention, because the porous structure gives birth to high surface area to volume ratios and creates a confined reaction environment that improves the reaction kinetics [14,15]. Moreover, the non-zero dimensional nanostructure makes the porous nanocrystals less vulnerable to dissolution, Ostwald ripening, and aggregation during * Corresponding author.…”

“…As a result, the combination of alloying and porous structure can be expected to be a promising candidate for the development of efficient ORR electrocatalysts, which has been proved by several very recent successful examples [9,10,15,16,18]. Hong et al prepared Pd-Pt alloy hollow nanostructures by sacrificial template method [9].…”

“…The obtained octahedral Pd-Pt alloy hollow nanostructures showed superior ORR activity than that of the Pt-on-Pd nanodendrites and commercial Pt/C catalyst. Besides, Snyder et al synthesized porous PtNi nanoalloys by dealloying method which is another frequently used pathway in the preparation of porous alloys [15]. In the preparation, Ni-rich solid PtNi nanoalloys were first synthesized, and then most of Ni atoms were dissolved in acid by potential cycling (a dealloying treatment), and finally porous Pt-rich PtNi nanoalloys were obtained.…”

Octahedral PtNi nanoparticles with controlled surface structure and composition for oxygen reduction reaction

“…Based on the above results and discussion, we found that in our present system, the use of high reaction temperature (200°C and reaction at a pre-heated oven), use of benzoic acid, and DMF as the solely solvent played crucial role in the synthesis of highly mondisperse, surfactant-free octahedral PtxNi1−x nanoparticles. Generally, the high temperature could effectively separate the crystal nucleation and the subsequent growth phases, which resulted in monodisperse nanocrystals [25]. The presence of benzoic acid could greatly improve the yield of octahedral nanoparticles with well-defined (111) facets.…”