Constructing Co–N–C Catalyst via a Double Crosslinking Hydrogel Strategy for Enhanced Oxygen Reduction Catalysis in Fuel Cells

Abstract

Exploiting platinum‐group‐metal (PGM)‐free electrocatalysts with remarkable activity and stability toward oxygen reduction reaction (ORR) is of significant importance to the large‐scale commercialization of proton exchange membrane fuel cells (PEMFCs). Here, a high‐performance and anti‐Fenton reaction cobalt–nitrogen–carbon (Co–N–C) catalyst is reported via employing double crosslinking (DC) hydrogel strategy, which consists of the chemical crosslinking between acrylic acid (AA) and acrylamide (AM) copolymerization and metal coordinated crosslinking between Co2+ and P(AA–AM) copolymer. The resultant DC hydrogel can benefit the Co2+ dispersion via chelated Co‐N/O bonds and relieve metal agglomeration during the subsequent pyrolysis, resulting in the atomically dispersed Co‐Nx/C active sites. By optimizing the ratio of AA/AM, the optimal P(AA–AM)(5‐1)–Co–N catalyst exhibits a high content of nitrogen doping (12.36 at%) and specific surface area (1397 m2 g−1), significantly larger than that of the PAA–Co–N catalyst (10.59 at%/746 m2 g−1) derived from single crosslinking (SC) hydrogel. The electrochemical measurements reveal that P(AA–AM)(5‐1)–Co–N possesses enhanced ORR activity (half‐wave potential (E1/2) ≈0.820 V versus the reversible hydrogen electrode (RHE)) and stability (≈4 mV shift in E1/2 after 5000 potential cycles in 0.5 m H2SO4 at 60 ºC) relative to PAA‐Co‐N, which is higher than most Co–N–C catalysts reported so far.

Unravelling Temperature Ramping Rates in Fabricating NaCl‐Induced Porous Co/N‐C Electrocatalysts for Oxygen Reduction Reaction

“…The value of I D /I G is an indicator of defects in graphene. [21] Thus, increased I D /I G value of Co/NÀ C-2, Co/NÀ C-5 and Co/NÀ C-10 indicates increased defects formed with rapid ramping rates, which is in accordance with the results from XRD that increased ramping rates reduce the aromatization between urea and glucose. Besides, the areas of D' peak increase with the increased ramping rate, implying enhanced stacking disorder of the graphene layers.…”

“…As shown in Figure 3b, the deconvoluted Raman spectra contain four peaks including I peak, D peak, D' peak and G peak, of which G peak refers to the sp 2 -hybridized carbon atoms in an ideal graphene, D' peak reflects the stacking disorder of the graphene layers, and D peak refers to the sp 3hybridized or doping atom-derived defects. [21] The intensity ratios of D peak to G peak (I D /I G ) for Co/NÀ C-2, Co/NÀ C-5 and Co/NÀ C-10 are 1.03, 1.12 and 1.14. The value of I D /I G is an indicator of defects in graphene.…”

Recent Advances in ZIF‐Derived Atomic Metal–N–C Electrocatalysts for Oxygen Reduction Reaction: Synthetic Strategies, Active Centers, and Stabilities

“…The contents of doped Co remarkably affect the catalytic performance of final electrocatalysts when using ZIFs as precursors. [46,47] In the past, Co-based ZIF-67 were always used as precursors to synthesize M-N-C. However, the high content of Co easily leads to form Co nanoparticles in the Co-N-C electrocatalysts.…”

Facile synthesis of cobalt cluster-CoNx composites: synergistic effect boosts electrochemical oxygen reduction

“…CoN x , Co n S m , Co n C m , Co n O m , etc. , 22–33 which have been well exploited in ORR investigations for potential applications in alkaline-based fuel cells and metal–air batteries. 34 However, many disadvantages have generally emerged to limit their further applications, caused by the complicated synthetic process of cobalt-based electrocatalysts, e.g.…”