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In a recent report, we demonstrated that few-nanometer-thick yttria-stabilized zirconia (YSZ) coating on a porous Pt cathode of a solid oxide fuel cell is an excellent facilitator of oxygen reduction reaction (ORR) kinetics and an effective suppressor of Pt agglomeration. In this article, we reveal the actual role of the YSZ overcoat in the ORR process through a series of electrochemical analyses. Without the overcoat, the nanoporous Pt is significantly agglomerated during a high-temperature operation and the ORR becomes limited by the availability of triple phase boundaries (TPBs). An ultrathin YSZ overcoat prevents the ORR process from being limited by TPB area by preserving the morphology of its underlying Pt layer. More importantly, the overcoat acts as an excellent facilitator of the atomic-oxygen-species-mediated chemical process(es) that used to be rate-limiting in the ORR of a noncoated Pt/YSZ system.

Transition metal oxides (TMOs) anchored on a carbon nanostructure have been widely pursued for oxygen reduction reaction (ORR) catalysis. The high ORR activity of TMO/graphene has been often attributed to the synergistic nature between TMO and carbon but with little relevant mechanistic study. In this report, the focus is made on how the type of majority oxygen-containing functional group of graphene affects the ORR performance of the resulting TMO/graphene nanocomposites. Our TiO 2 /carboxylated graphene and ZrO 2 / hydroxylated graphene rendered an ORR activity very close to that of Pt/C with an equal mass loading, via a four-electron transfer dominant process unlike other TMO/graphene variants of study. It is revealed that a stable anchoring of nanoparticles (NPs) on the graphene surface, which is essential to prevent the restacking of graphene layers, is established only through a specific type of functional groups on the graphene. In addition, the interplay among TMOs, graphene, and functional groups is found to be deterministic in the activity and electron transfer pathway of ORR, which is supported by density function theory (DFT) calculations. The calculations indicate that the electron transfer pathway is dependent upon the structure of NPs interfacing with functional groups of the graphene as it affects the preferred sites for oxygen dissociation.

In this report, we present a study of using nitrogen‐doped graphene as the air electrode of low temperature solid oxide fuel cells (LT‐SOFCs) operating at 350 °C or lower. Three graphene derivatives were prepared through hydrothermal reactions and their electrochemical performance and material properties were characterized in the temperature range of 225–350 °C in atmospheric air. Nitrogen‐doped graphene was found to exhibit a decent air electrode performance comparable to a porous Pt electrode aged for 8 h at 350 °C, but only for a limited time. After ∼10 h of operation at 350 °C, the electrode performance degraded significantly due to carbon oxidation. However, alternative routes of synthesizing/doping graphene derivatives are expected to improve the viability of using these materials as a practical high temperature air electrode.