Exploring the Potential of Heteroatom-Doped Graphene Nanoribbons as a Catalyst for Oxygen Reduction.

In this study, we created a series of N, S, and P-doped and co-doped carbon catalysts using a single graphene nanoribbon (GNR) matrix and thoroughly evaluated the impact of doping on ORR activity and selectivity in acidic, neutral, and alkaline conditions. The results obtained showed no significant changes in the GNR structure after the doping process, though changes were observed in the surface chemistry in view of the heteroatom insertion and oxygen depletion. Of all the dopants investigated, nitrogen (mainly in the form of pyrrolic-N and graphitic-N) was the most easily inserted and detected in the carbon matrix. The electrochemical analyses conducted showed that doping impacted the performance of the catalyst in ORR through changes in the chemical composition of the catalyst, as well as in the double-layer capacitance and electrochemically accessible surface area. In terms of selectivity, GNR doped with phosphorus and sulfur favored the 2e- ORR pathway, while nitrogen favored the 4e- ORR pathway. These findings can provide useful insights into the design of more efficient and versatile catalytic materials for ORR in different electrolyte solutions, based on functionalized carbon.

Using Palladium and Gold Palladium Nanoparticles Decorated with Molybdenum Oxide for Versatile Hydrogen Peroxide Electroproduction on Graphene Nanoribbons.

Electrocatalytic production of H2O2 via a two-electron oxygen reduction reaction (ORR-2e-) is regarded as a highly promising decentralized and environmentally friendly mechanism for the production of this important chemical commodity. However, the underlying challenges related to the development of catalytic materials that contain zero or low content of noble metals and that are relatively more active, selective, and resistant for long-term use have become a huge obstacle for the electroproduction of H2O2 on commercial and industrial scales. The present study reports the synthesis and characterization of low metal-loaded (≤6.4 wt %) catalysts and their efficiency in H2O2 electroproduction. The catalysts were constructed using gold palladium molybdenum oxide (AuPdMoOx) and palladium molybdenum oxide (PdMoOx) nanoparticles supported on graphene nanoribbons. Based on the application of a rotating ring-disk electrode, we conducted a thorough comparative analysis of the electrocatalytic performance of the catalysts in the ORR under acidic and alkaline media. The proposed catalysts exhibited high catalytic activity (ca. 0.08 mA gnoble metal-1 in an acidic medium and ca. 6.6 mA gnoble metal-1 in an alkaline medium), good selectivity (over 80%), and improved long-term stability toward ORR-2e-. The results obtained showed that the enhanced ORR activity presented by the catalysts, which occurred preferentially via the two-electron pathway, was promoted by a combination of factors including geometry, Pd content, interparticle distance, and site-blocking effects, while the electrochemical stability of the catalysts may have been enhanced by the presence of MoOx.

Highly Electroactive Ni Pyrophosphate/Pt Catalyst toward Hydrogen Evolution Reaction.

Robust electrocatalysts toward the resourceful and sustainable generation of hydrogen by splitting of water via electrocatalytic hydrogen evolution reaction (HER) are a prerequisite to realize high-efficiency energy research. Highly electroactive catalysts for hydrogen production with ultralow loading of platinum (Pt) have been under exhaustive exploration to make them cutting-edge and cost-effectively reasonable for water splitting. Herein, we report the synthesis of hierarchically structured nickel pyrophosphate (ß-Ni2P2O7) by a precipitation method and nickel phosphate (Ni3(PO4)2) by two different synthetic routes, namely, simple cost-effective precipitation and solution combustion processes. Thereafter, Pt-decorated nickel pyrophosphate and nickel phosphate (ß-Ni2P2O7/Pt and Ni3(PO4)2/Pt) were prepared by using potassium hexachloroplatinate and ascorbic acid. The fabricated novel nickel pyrophosphate and nickel phosphate/Pt materials were utilized as potential and affordable electrocatalysts for HER by water splitting. The detailed electrochemical studies revealed that the ß-Ni2P2O7/Pt (1 µg·cm-2 Pt) electrocatalyst showed excellent electrocatalytic performances for HER in acidic solution with an overpotential of 28 mV at -10 mA·cm-2, a Tafel slope of 32 mV·dec, and an exchange current density ( j0) of -1.31 mA·cm-2, which were close to the values obtained using the Vulcan/Pt (8.0 µg·cm-2 Pt), commercial benchmarking electrocatalyst with eight times higher Pt amount. Furthermore, the ß-Ni2P2O7/Pt electrocatalyst maintains an excellent stability for over -0.1 V versus RHE for 12 days, keeping j0 equal after the stability test (-1.28 mA cm-2). Very well-distributed Pt NPs inside the "cages" on the ß-Ni2P2O7 structure with a crystalline pattern of 0.67 nm distance to the Ni2P2O7/Pt electrocatalyst, helping the Volmer-Tafel mechanism with the Tafel reaction as a major rate-limiting step, help to liberate very fast the Pt sites after HER. The high electrocatalytic performance and remarkable durability showed the ß-Ni2P2O7/Pt material to be a promising cost-effective electrocatalyst for hydrogen production.