Toward Highly Stable Electrocatalysts via Nanoparticle Pore Confinement

Abstract

The durability of electrode materials is a limiting parameter for many electrochemical energy conversion systems. In particular, electrocatalysts for the essential oxygen reduction reaction (ORR) present some of the most challenging instability issues shortening their practical lifetime. Here, we report a mesostructured graphitic carbon support, Hollow Graphitic Spheres (HGS) with a specific surface area exceeding 1000 m(2) g(-1) and precisely controlled pore structure, that was specifically developed to overcome the long-term catalyst degradation, while still sustaining high activity. The synthetic pathway leads to platinum nanoparticles of approximately 3 to 4 nm size encapsulated in the HGS pore structure that are stable at 850 °C and, more importantly, during simulated accelerated electrochemical aging. Moreover, the high stability of the cathode electrocatalyst is also retained in a fully assembled polymer electrolyte membrane fuel cell (PEMFC). Identical location scanning and scanning transmission electron microscopy (IL-SEM and IL-STEM) conclusively proved that during electrochemical cycling the encapsulation significantly suppresses detachment and agglomeration of Pt nanoparticles, two of the major degradation mechanisms in fuel cell catalysts of this particle size. Thus, beyond providing an improved electrocatalyst, this study describes the blueprint for targeted improvement of fuel cell catalysts by design of the carbon support.

Review—Electromobility: Batteries or Fuel Cells?

“…138 The future challenge for ORR catalyst development is to combine high mass activity catalyst concepts with more stable low-surface area graphitized carbon-supports. Alternative support materials have also been considered such as carbon nanotubes, 135 hollow graphitic spheres, 140 and conductive metal oxides. 141 Recently, Inaba et al published MEA measurements with SiO 2 nanofiber supported Pt, 142 showing reasonable performance at intermediate humidification and poor performance under other commonly employed operating conditions.…”

Future Challenges in Heterogeneous Catalysis: Understanding Catalysts under Dynamic Reaction Conditions

“…These highly porous supports may increase the stability of the catalyst against coking at temperatures above 800 °C in the dry reforming of methane 121. In another approach, Pt‐based nanoparticles were specifically deposited in the mesopore system of a support122 or within graphitized carbon hollow spheres 123. The incorporation of nanostructured, bifunctional Co‐particles into a zeolite matrix resulted in an increased stability under operating conditions of the Fischer–Tropsch synthesis attributed to reduced mobility due to pore confinement effects 124.…”

Biohydrogen for a New Generation of H2/O2 Biofuel Cells: A Sustainable Energy Perspective

“…These metals are, however, very expensive (average price is 40 E/g against 2 E/g for Ru for example [from http://www.platinum.matthey.com/prices/price-charts/]), are available in low amounts on earth (37 ppb in the Earth's crust), and are nonbiodegradable. Extensive research has aimed at decreasing the Pt content (for a review see [5] ), such as: 1) nanostructuration of the catalysts, [6,7] 2) use of alloys or heterostructures, [8][9] 3) nanostructuration and treatment of the carbon support, [10][11][12][13] 4) use of noncarbon matrixes such as conducting polymers, [14] and 5) use of semiconductive transitionmetals. [15] Furthermore, platinum catalysts are readily poisoned by very low levels of CO and S (0.1 % of CO is sufficient to decrease one hundred fold the catalytic activity of Pt in ten minutes), thus requiring extensive H 2 purification.…”