Stability and activity of platinum nanoparticles in the oxygen electroreduction reaction: is size or uniformity of primary importance?

Kirill O Paperzh,Anastasia A Alekseenko,Vladimir E Guterman,Olga A Safronenko,Ilya V Pankov,Vadim A Volochaev

doi:10.3762/bjnano.12.49

Abstract

Platinum–carbon catalysts are widely used in the manufacturing of proton-exchange membrane fuel cells. Increasing Pt/C activity and stability is an urgent task and the optimization of their structure seems to be one of the possible solutions. In the present paper, Pt/C electrocatalysts containing small (2–2.6 nm) nanoparticles (NPs) of a similar size, uniformly distributed over the surface of a carbon support, were obtained by the original method of liquid-phase synthesis. A comparative study of the structural characteristics, catalytic activity in the oxygen electroreduction reaction (ORR), and durability of the synthesized catalysts, as well as their commercial analogs, was carried out. It was shown that the uniformity of the structural and morphological characteristics of Pt/C catalysts makes it possible to reduce the negative effect of the small size of NPs on their stability. As a result, the obtained catalysts were significantly superior to their commercial analogs regarding ORR activity, but not inferior to them in terms of stability.

Highlights

Nowadays, low-temperature proton-exchange membrane fuel cells (PEMFC) are gaining a wider application
It is important to note that at a similar degradation rate (ESA decrease during the stress test) the Pt/C catalysts that we have synthesized demonstrated an oxygen electroreduction reaction (ORR) mass activity which exceeded the mass activity of the commercial Pt/C analogs by approx. 30–60%, both in the initial state and upon completion of the stress test
Due to the smaller size and higher uniformity of the NP spatial distribution, the G series catalysts are characterized by higher electrochemically active surface area (ESA) values (from 120 to 88 m2·g−1(Pt)) than the commercial Pt/C catalysts JM20 and JM40 (Johnson Matthey) (84 and 67 m2·g−1(Pt)), which contained 20 and 40 wt % of platinum, respectively

Summary

Introduction

Low-temperature proton-exchange membrane fuel cells (PEMFC) are gaining a wider application. The opposite effect of the NP size on the specific activity, stability, and ESA of the catalysts forces us to seek a compromise or, in other words, to seek structures with an optimal combination of catalyst mass activity and stability In this regard, of particular interest are the methods for the synthesis of catalysts, which make it possible to obtain materials that combine small size of the nanoparticles, their narrow dimensional and uniform spatial distribution over the surface, and pores of support. It is due to several factors: some nanoparticles can consist of several crystallites, so they have a larger size [19]; differences in the principles of calculation, which serve as the basis for the corresponding research methods [41]; a possible contribution of NP structural defects to the broadening of the X-ray diffraction pattern maxima [42], and problems related to the recognition of ultrasmall particles in TEM micrographs.

G20 G25 G30 G35 G40 JM20 JM40

Findings

Conclusion