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Porous Iron-Tungsten Carbide Electrocatalyst with High Activity and Stability toward Oxygen Reduction Reaction: From the Self-Assisted Synthetic Mechanism to Its Active-Species Probing

Song, Li, Wang, Tao, Wang, Yilin, Xue, Hairong, Fan, Xiaoli, Guo, Hu, Xia, Wei, Gong, Hao, He, Jianping
ACS Applied Materials & Interfaces 2017 v.9 no.4 pp. 3713-3722
X-ray diffraction, chlorides, durability, electrochemistry, graphene, ions, iron, methanol, nanocomposites, oxygen, pyrolysis, temperature, tungsten
We synthesized a novel nonprecious metal electrocatalyst by pyrolysis of a colloid mixture consisting of a tungsten source and phenolic resin, with the simultaneous addition of ferric salt. The rationally designed electrocatalyst has a unique structure, with nanosized WC and Fe₃W₃C uniformly dispersed in a three-dimensional porous carbon framework. WC, which was thought difficult to produce, is successfully prepared at a relatively low temperature of about 750 °C at an inert atmosphere. XRD studies demonstrate the self-assisted effect of Fe, which accelerates the formation of WC, getting around the pathway of direct carbonaceous reduction of tungsten by carbon. The porous iron-tungsten carbide (Fe-W-C) nanocomposite as electrocatalyst shows excellent ORR activity with the onset and half-wave potentials of 0.864 and 0.727 V (vs RHE), respectively, which are close to those of Pt/C (0.976 and 0.820 V vs RHE). Electrochemical measurements show that Fe-W-C follows almost the effective four-electron-transfer pathway and would not be disturbed by methanol. The presence of a protective graphite shell outside the active carbide cores substantially improves the durability of the electrocatalyst. Both the removal of Fe species and the absence of W species would severely degrade the activity, while halide ions Cl– and sulfur-containing species SCN– can significantly suppress the ORR activity by the blocking of Fe species. These facts indicate that the ORR active species of Fe-W-C should be relevant to both W and Fe species.