Phase engineering of PtCo alloy supported on N-doped carbon via pyrolysis of ZIF and carbon black for efficient and durable oxygen reduction reaction

Abstract

Highly ordered Pt alloy structure is an effective method to improve the catalytic activity and stability of cathodic oxygen reduction reaction (ORR) in acidic media, which is of great significance for the large-scale commercial application of proton exchange membrane fuel cells (PEMFCs). Herein, a highly efficient and durable catalyst composed of structurally ordered PtCo alloys with nitrogen-doped carbon (NC) shells is designed by improving the impregnation reduction method, using an intermediate self-sacrificial template strategy. Under the optimal preparation conditions of 20 wt% doped Ketjen black and a calcination temperature of 850 °C, the ordered PtCo alloy-based catalyst (denoted as L1₀-PtCo/ZNC) is obtained with an average nanoalloy size of about 3.9 nm and uniformly loaded on the N-doped carbon support via pyrolysis of cobalt-based zeolite imidazolate framework (ZIF-67) and carbon black. The half-wave potential (E_1/2) of L1₀-PtCo/ZNC reaches 0.927 V vs. RHE, outperforming most of the reported catalysts and the benchmark commercial Pt/C catalyst. Moreover, the mass activity (MA, 1.06 A mg_Pt^-1) and specific activity (SA, 1.03 mA cm^-2_Pt) of L1₀-PtCo/ZNC are 7.6 and 4.7 times of those of Pt/C, respectively. The MA and SA values of L1₀-PtCo/ZNC after 10,000 cycles are 35 and 23 times of those of Pt/C catalysts, respectively, indicative of the excellent durability of L1₀-PtCo/ZNC. This method provides an effective strategy in preparing highly active and stable ordered PtCo alloy-based hybrid catalysts for acid ORR.