Highly Porous Polypyrrole (PPy) Hydrogel Support for the Design of a Co–N–C Electrocatalyst for Oxygen Reduction Reaction

Abstract

Atomically dispersed metal−nitrogen−carbon (M−N− C) catalysts have emerged as one of the most promising platinum-group metal (PGM)-free cathode catalysts for oxygen reduction reaction (ORR). Among the various approaches to enhance the ORR performance of the catalysts, increasing the density of accessible active sites is of paramount importance. Thus, nitrogen-rich support with abundant porosity can be very propitious. Herein, we report a highly porous polypyrrole (PPy) hydrogel as a versatile support for the facile design of a Co−N−C electrocatalyst for ORR. The resulting Co−N−C catalyst with abundant micro-and mesoporous combinations demonstrates a half-wave potential (E 1/2 ) of 0.825 V vs reversible hydrogen electrode (RHE) in O 2 -saturated 0.1M KOH with just 2.1 wt % Co content. The ORR performance reduces only 11 mV (E 1/2 ) after 5000 cycles of accelerated durability test (ADT), portraying its excellent stability. The catalyst retains ≈83% of its original current during a short-term durability test at 0.8 V vs RHE for 25 h. Furthermore, the catalyst shows electron transfer approaching ≈4 with low H 2 O 2 yield in the potential range 0.5−0.9 V vs RHE. This work provides a simple design strategy to synthesize M−N−C catalysts with increased accessible active site density and enhanced mass transport for ORR and other electrocatalytic applications.

A Metal–Organic Framework-Derived Atomically Dispersed Yttrium as an Electrocatalyst for Oxygen Reduction Reaction

“…Design of efficient and cost-effective platinum group metal (PGM)-free electrocatalysts to boost the otherwise sluggish kinetics of oxygen reduction reaction (ORR) is a key challenge in energy storage and conversion devices. − Many catalyst design attempts have been made recently toward low-cost alternatives. , One of the attempts to replace PGMs has brought about a new class of bioinspired catalysts called single-atom catalysts (SACs) which consist of atomically dispersed metal centers coordinated to nitrogen atoms on a partially graphitized carbon support (MNxCy or M–N–C). − A plethora of works have been carried out toward this approach involving nonprecious metal cations stabilized by nitrogen atoms in a porphyrin type environment. This has led to the development of SACs of 3d transition metals (Fe, − Co, − Mn, , Cu, etc.) and p-block elements such as Sn, Sb, and Se as well, primarily serving as potential candidates in electrochemical applications.…”

A Hybrid Hydrogel Approach for the Design of N, S Dual-Doped Porous Carbon Electrocatalyst for Oxygen Reduction Reaction

“…Intensive investigation in this arena has yielded various nonprecious metals (NPMs) and metal-free materials as potential alternatives . Compounds of transition metals such as oxides, nitrides, sulfides, phosphides, hydroxides, etc., despite catalyzing the ORR in alkaline medium, still require improvement in their activity, stability, and utilization efficiency. , As another alternative, metal–nitrogen–carbon-based electrocatalysts with isolated single atoms of transition and p-block elements coordinated to N atoms have emerged as potential candidates for the ORR. − Although this class of catalysts, also called single-atom catalysts (SACs), has demonstrated excellent ORR activity, it still suffers from limited stability due to the demetalation of metal atoms from the active sites and the restricted utilization of the M–N–C active centers due to the lack of adequate porosity. − The demetalation issue also persists in alkaline medium under ORR condition …”