Effect of Catalyst Pore Size on the Performance of Non‐Precious Fe/N/C‐Based Electrocatalysts for High‐Temperature Polymer Electrolyte Membrane Fuel Cells

Abstract

Owing to the high cost of technologies utilizing the oxygen reduction reaction (ORR) in fuel cell applications, considerable efforts have been recently made to develop non-precious metal electrocatalysts for the commercialization of the low-temperature polymer electrolyte membrane fuel cells (LT-PEMFCs). By extension, non-precious-metal electrocatalysts can be a costeffective solution for the commercialization of high-temperature PEMFCs (HT-PEMFCs). However, no previous reports have been published regarding the applicability. Herein, we demonstrate that a hierarchical mesoporous iron and nitrogen co-doped carbon (Fe/N/C) electrocatalyst is able to efficiently electrocatalyze the ORR in a phosphoric acid electrolyte with a halfwave potential of 0.72 V (only 170 mV deviation from conventional Pt/C) and high selectivity (electron-transfer number > 3.95) with a mild overpotential. Furthermore, we fabricated HT-PEMFC devices on the basis of hierarchical mesoporous Fe/ N/C electrocatalysts and non-aqueous electrolytes, which exhibited a high performance, over 20 mW/cm 2 . Besides, the optimal hierarchical porosity of the mesoporous Fe/N/C catalyst contributes to its high ORR activity. It is considered that it provides a large surface area for electrocatalytic ORR, and improves the proton and oxygen transport properties.There has been a growing need for clean and sustainable hydrogen energy and fuel cell commercialization and technologies. Depending on the operating temperature, two types of polymer electrolyte membrane fuel cells (PEMFCs) exist: hightemperature PEMFCs (HT-PEMFCs) and low-temperature PEFMCs (LT-PEMFCs). HT-PEMFC operation in the temperature range of 100-200 8C has various advantages over LT-PEMFCs, [1] including cogeneration of power and heat, no need for water management, and a high tolerance to carbon monoxide (CO) fuel impurities. [2a,b] An additional radiator for heat removal is necessary for LT-PEMFCs; otherwise, the high-temperature operating conditions degrade the LT-PEMFC components. In contrast, generated heat can be used to aid other processes in HT-PEMFCs. One of the reasons of low oxygen reduction reaction (ORR) kinetics with LT-PEMFCs is due to the low temperature operation. By increasing the operating temperature of the fuel cell, the reaction kinetics and the diffusion of reactant gas and product gas increase.Additionally, the LT-PEMFC requires a humidifier and management of water flooding and discharging, which should be taken into consideration; [3] liquid water blocks the electrochemically active site and high humidity is required for proton conductivity of the perfluorinated sulfonic acid polymer membrane (e. g. Nafion) in LT-PEMFC. On the other hand, HT-PEMFCs do not require a humidifier, which simplifies the system.CO tolerance is one of the crucial factors for a practical system because additional purification of hydrogen gas is needed if the catalyst cannot endure chemical poisoning by CO. State-of-the-art platinum-based catalysts are known to be vulnerable to CO poisoning [4] ;...

Reconstruction of Electronic Structure of MOF-525 via Metalloporphyrin for Enhanced Photoelectro-Fenton Process

“…But the BET calculation of specific surface area is mainly based on the micropores, which results in a slight decrease of MOF-525-Fe/Zr specific surface area compared with MOF-525. Meanwhile, it can be seen that the multistage pore structure further enlarges the pore volume of MOF-525-Fe/Zr [36,37].…”

Importance of Electrocatalyst Morphology for the Oxygen Reduction Reaction

“…[45,194] Among these templates, the SiO 2 nanospheres and SBA-15 are commonly used hard templates. [195][196][197] The replica of these porous materials using metal or carbon precursors generates porous metal oxides or NÀ C materials, after which the hard templates are removed. For instance, Liang et al described a hardtemplating method to synthesize 3D MÀ NÀ C electrocatalysts with porous structures, which are formed by the removal of hard templates ( Figure 10).…”

“…All kinds of porous M−N−C materials can be synthesized by taking full advantages of the diversity of templates ,. Among these templates, the SiO 2 nanospheres and SBA‐15 are commonly used hard templates . The replica of these porous materials using metal or carbon precursors generates porous metal oxides or N−C materials, after which the hard templates are removed.…”

High-Efficiency Combined Heat and Power through a High-Temperature Polymer Electrolyte Membrane Fuel Cell and Gas Turbine Hybrid System

“…The research into catalysts has focused on improving platinum group material-based components by studying innovative alloys [62,63], improving carbon support with carbon doping [64][65][66][67] and polymer wrapping [68], and modifying the catalyst layer structure [69]. Moreover, alternative catalyst platinum-group materials have been studied, obtaining promising results [70][71][72][73][74]. Phosphoric Acid (PA) -doped polybenzimidazole (PBI) membranes represent the state-of-the-art material for HT-PEMFCs membranes, given their high conductivity and excellent thermal stability, and the low PA vapor pressure at high temperatures.…”