Constructing a Triple-Phase Interface in Micropores to Boost Performance of Fe/N/C Catalysts for Direct Methanol Fuel Cells Yu-Cheng Wang,† Long Huang,†,‡ Pu Zhang,† Yi-Ting Qiu,† Tian Sheng,† Zhi-You Zhou,*,† Gang Wang,§ Jian-Guo Liu,*,§ Muhammad Rauf,† Zheng-Qiang Gu,† Wei-Tai Wu,† and Shi-Gang Sun*,† †
State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China ‡ Kunming Sino-Platinum Metals Catalyst Co. Ltd., Kunming 650106, China § National Laboratory of Solid State Microstructures, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China S Supporting Information *
ABSTRACT: Pyrolyzed Fe/N/C, a promising nonpreciousmetal catalyst for oxygen reduction reaction (ORR), usually relies on abundant micropores, which can host a large amount of active sites. However, microporous structure suffers from severe water flooding to break the triple-phase interface where ORR occurs, especially in a direct methanol fuel cell (DMFC) fed with liquid fuel. Current studies about the fabrication of a triple-phase interface are mainly limited on a Pt/C catalyst layer, where mesopores and macropores are concerned. Here, we successfully constructed a triplephase interface in micropores of Fe/N/C catalysts by controlling the distribution of a hydrophobic additive, dimethyl silicon oil (DMS), just partially penetrating into the micropores. The elaborately constructed Fe/N/C-based DMFC can deliver high power density (102 and 130 mW cm−2 at 60 and 80 °C, respectively) and durability comparable to that of Pt/C-based DMFC. This study presents a new avenue to engineer catalyst microporous channels to boost the performance of nonprecious-metal catalysts for fuel cells.
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blocked by water, which impedes the O2 transport to active sites, thus breaking the triple-phase interface.10,11 Water flooding becomes more problematic in direct methanol fuel cells (DMFCs), where severe crossover of methanol and water from the anode to cathode occurs.12 To construct a good triple-phase interface in the catalyst layer, it needs to build robust oxygen-transport channels to active sites.13 This has been extensively studied for Pt-based catalyst layers. For example, various hydrophobic additives (i.e., dimethyl silicon oil, microsphere Teflon) were introduced to serve as a hydrophobic phase for O2 transport within pores ranging from 20 nm to 1.00 μm, which act as main masstransport channels in Pt/C catalyst layers.14−16 These studies mainly focus on the fabrication of a triple-phase interface on the scale of mesopores and macropores. However, rare studies involve engineering a triple-phase interface in the micropores
he bottleneck for fuel cell commercialization is high cost, which mainly comes from the expensive Pt catalysts. Developing nonprecious-metal catalysts is an effective approach to reduce the cost. Currently, Fe/N/C catalysts, derived from high-temperature pyrolysis of the mixture of iron salt, nitrogen-containing species, and carbon support, have been considered as the most promising nonprecious-metal catalyst to replace Pt for oxygen reduction reaction (ORR) in fuel cells.1 Highly active Fe/N/C catalysts usually rely on abundant micropores because they can host a large amount of active sites.2−6 However, such a microporous structure of Fe/N/C catalysts also causes some problems, such as water flooding.7,8 In the cathode catalyst layer of fuel cells, ORR (O2 + 4H+ + 4e → H2O) only occurs at the triple-phase interface, where gas (O2), electrolyte (i.e., Nafion that provides H+), and electrically connected catalyst active sites contact together.9 As for Fe/N/ C catalysts, most of the active sites are located in micropores. Due to the small pore size (
