Chemical Vapor Deposition of Fe-N-C Oxygen Reduction Catalysts with Full Utilization of Dense Fe-N4 Sites

Abstract

Replacing scarce and expensive platinum (Pt) with metal-nitrogen-carbon (M-N-C) catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) has largely been impeded by the low activity of M-N-C, in turn limited by low site density and low site utilization. Herein, we overcome these limits by implementing chemical vapor deposition (CVD) to synthesize Fe-N-C, an approach fundamentally different from previous routes. The Fe-N-C catalyst, prepared by flowing iron chloride vapor above a N-C substrate at 750 ℃, has a record Fe-N<sub>4</sub> site density of 2×10<sup>20</sup> sites·gram<sup>-1</sup> with 100% site utilization. A combination of characterizations shows that the Fe-N<sub>4</sub> sites formed via CVD are located exclusively on the outer-surface, accessible by air, and electrochemically active. This catalyst delivers an unprecedented current density of 33 mA·cm<sup>-2</sup> at 0.90 V<i><sub>i</sub></i><sub>R-free</sub> (<i>iR</i>-corrected) in an H<sub>2</sub>-O<sub>2</sub> PEMFC at 1.0 bar and 80 ℃.

Molten NaCl‐Assisted Synthesis of Porous Fe‐N‐C Electrocatalysts with a High Density of Catalytically Accessible FeN4 Active Sites and Outstanding Oxygen Reduction Reaction Performance

“…The utilization rate of FeN 4 sites can be defined as the ratio between the SD of accessible FeN 4 sites and overall FeN 4 sites in the Fe-N-C materials. [9] In typical rotating disk electrode (RDE) tests, the utilization rate of FeN 4 sites in Fe-N-C electrocatalysts (Fe loading ≈3.0 wt%) is generally below 10%, meaning that the effective Fe loading for ORR is only ≈0.3 wt%. [6b,8a] Thus, engineering the morphology of Fe-N-C electrocatalysts to maximize reactant accessibility to FeN 4 active sites is key to achieving efficient ORR performance at low metal catalyst loadings.…”

Nitrogen-Doped Carbons Derived from Imidazole-Based Cross-Linked Porous Organic Polymers

“…Indeed, N-doped porous carbons are able to coordinate single transition metal ions (e.g., Fe, Co, Cu, Mn, etc.) by pyridinic or pyrrolic nitrogen functionalities and yield unique catalytic materials of many advanced applications, including (electro)catalysis (as an alternative to expensive precious metals [22,23]), medicine (as artificial enzymes [24]), and separation and purification processes (e.g., as materials for wastewater remediation [25]). In this report, we show that polycondensation of phloroglucinol with imidazole-2-carboxaldehyde yields porous organic polymers and ultramicroporous carbons with N-content of up to 16 and 12 wt.%, respectively, while polycondensation with 2-thiazolecarboxaldehyde is a facile approach to synthesize N and S co-doped carbons (N,S-co-doping).…”