N-Doped Hollow Carbon Sphere and Polyhedral Carbon Composite Supported Pt/Fe Nanoparticles as Highly Efficient Cathodic Catalysts of Proton-Exchange Membrane Fuel Cells

With the growing energy crisis, people urgently need green energy sources to replace fossil ones. As a zero-emission clean energy source, the proton-exchange membrane fuel cell (PEMFC) has received growing attention from researchers due to its broad practical application. However, so far only noble metal Pt can be used as a mature cathodic catalyst for PEMFC to effectively promote the slow kinetic process of the oxygen reduction reaction (ORR). Herein, a low Pt-loading carbon-based catalyst (pCN@NHCS-Fe/Pt-280) with hollow carbon spheres (HCSs), metal-organic frameworks (MOFs), and carbon nanotubes (CNTs) structure was synthesized by the thermal reduction of platinum acetylacetonate and pCN@NHCS-Fe. Compared with the benchmark Pt/C catalyst, pCN@NHCS-Fe/Pt280 presents low cost, and its ORR onset potential (Eonset = 0.971 VRHE) and half-wave potential (E1/2 = 0.883 VRHE) in acidic media are comparable to those of 40% Pt/C (Eonset = 0.965 VRHE, E1/2 = 0.883 VRHE). In the durability test for ORR, its current retention percentage (92.3%) is still higher than 40% Pt/C (86.7%) after 10 000 s of the constant potential test, and its cyclic voltammetry (CV) and linear scan voltammetry (LSV) profiles after 500 cycles exhibit outstanding stability. Moreover, pCN@NHCS-Fe/Pt-280 quickly recovers to 79.1% of the initial value after adding methanol, while 40% Pt/C can recover only to 72.3%, indicating a superior ability in antialcohol oxidation. In addition, the maximum power density of pCN@NHCS-Fe/Pt-280 (518.7 mW cm-2) as the cathode catalyst of PEMFC in the H2-air cell test is also higher than that of Pt/C (515.3 mW cm-2), while its power density is lower than that of Pt/C in the H2-O2 cell test at different pressures due to the high-temperature influence at high current densities. This work provides a valuable idea for the design of multistructured (HCSs, MOFs, CNTs, etc.) electrocatalysts and a feasible strategy for the development of low-Pt-loaded ORR catalysts.