Mattia Saccoccio

A bi-functional catalyst for oxygen reduction and oxygen evolution reactions from used baby diapers: α-Fe2O3 wrapped in P and S dual doped graphitic carbon

The development of energy conversion and storage devices and the disposal of solid waste represent two major challenges for environmental sustainability. The development of many key sustainable energy technologies relies on fast oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics. However, both reactions are sluggish. In the present work, we address these two issues synergistically by fabricating Fe2O3 wrapped in P and S dual-doped graphitized carbon (Fe2O3/P–S-CG) from soiled baby diapers, whose disposal and recycling are beneficial to the environment. Electrochemical tests revealed that Fe2O3/P–S-GC has a significant catalytic activity towards both the ORR and OER in 0.1 M KOH. In particular, the difference between the ORR potential at 3 mA cm−2 and the OER potential at 10 mA cm−2 is as small as ∼0.86 V. This value is comparable to that of commercial precious metal-based catalysts. In addition, Fe2O3/P–S-GC exhibits a favorable catalytic durability, making it a promising bi-functional non-precious catalyst for the ORR and OER.

In situ preparation of Ca0.5Mn0.5O/C as a novel high-activity catalyst for the oxygen reduction reaction

Rock-salt-type MnO is rarely used as an electrocatalyst because of its relatively poor activity. Herein, through an in situ preparation and Ca-substitution of MnO/C, we were able to obtain a novel composite, i.e., Ca0.5Mn0.5O/C, as a highly active, stable, and cost-effective oxygen reduction reaction (ORR) catalyst in alkaline media. Ca0.5Mn0.5O/C and MnO/C share a similar rock-salt phase. In comparison to MnO/C, Ca0.5Mn0.5O/C follows a more effective four-electron pathway (versus a two-electron pathway) and displays higher ORR activity, including a more positive onset potential (by 0.05 V), a more positive half-wave potential (by 0.04 V), and a higher current density (by 1.48 mA cm−2). The Ca0.5Mn0.5O/C also shows comparable mass activity, higher activity per material cost, and superior stability in alkaline media in comparison to commercial Pt/C. Additionally, the as-prepared Ca0.5Mn0.5O/C exhibits higher ORR activity than the physical mixture of Ca0.5Mn0.5O and carbon. The enhanced ORR performance of Ca0.5Mn0.5O/C is likely due to (1) the presence of the divalent redox pair MnII/MnIII; (2) the formation of MnOOH on the Ca0.5Mn0.5O surface; and (3) a stronger synergistic interaction between Ca0.5Mn0.5O and C resulting from the in situ preparation method. This work provides new routes to develop advanced electrocatalysts using transition-metal-oxide/carbon composites.