One-Pot Self-Assembled, Reduced Graphene Oxide/Palladium Nanoparticle Hybrid Aerogels for Electrocatalytic Applications

Synthesis of Cobalt Complex Containing Trans-Cinnamate and Its Electrocatalytic Activity for Oxygen Evolution Reaction

There are many efforts reported on finding effective catalysts for oxygen evolution reactions (OERs), which are important reactions in the energy field. Coordination polymers, including metal–organic frameworks (MOFs), are attracting attention as electrocatalysts for OERs due to their versatility and modulating properties. A new cobalt complex containing trans-cinnamate and 2-aminopyridmidine ligands was synthesized using a hydrothermal method. The cobalt complex showed a 1D chain structure. The electrocatalytic activity and stability of the cobalt complex with or without an electrochemical supporter, such as reduced graphene oxide (rGO), OERs were investigated and compared with a metal oxide reference material. Due to the π-conjugated trans-cinnamate, which has electron flexibility near the Co centers, the catalyst/rGO composite showed significant catalytic activities, with an overpotential of 386 mV and a Tafel slope of 64 mV/dec.

Advances in Subcritical Hydro-/Solvothermal Processing of Graphene Materials

Many promising graphene-based materials are kept away from mainstream applications due to problems of scalability and environmental concerns in their processing. Hydro-/solvothermal techniques overwhelmingly satisfy both the aforementioned criteria, and have matured as alternatives to wet-chemical methods with advances made over the past few decades. The insolubility of graphene in many solvents poses considerable difficulties in their processing. In this context hydro-/solvothermal techniques present an ideal opportunity for processing of graphenic materials with their versatility in manipulating the physical and thermodynamic properties of the solvent. The flexibility in hydro-/solvothermal techniques for manipulation of solvent composition, temperature and pressure provides numerous handles to manipulate graphene-based materials during synthesis. This review provides a comprehensive look at the subcritical hydro-/solvothermal synthesis of graphene-based functional materials and their applications. Several key synthetic strategies governing the morphology and properties of the products such as temperature, pressure, and solvent effects are elaborated. Advances in the synthesis, doping, and functionalization of graphene in hydro-/solvothermal media are highlighted together with our perspectives in the field.

Fabrication of Graphene Aerogels with Heavily Loaded Metallic Nanoparticles

Natural biomaterials with hierarchical structures that enable extraordinary capability of detecting chemicals have inspired the interest in producing materials that can mimic these natural structures. This study reports the fabrication of hierarchically-structured, reduced graphene oxide (rGO) aerogels with heavily loaded palladium (Pd), platinum (Pt), nickel (Ni), and tin (Sn) metallic nanoparticles. Metal salts chelated with ethylenediaminetetraacetic acid (EDTA) were mixed with graphene oxide (GO) and then freeze-dried. The subsequent reduction produces rGO/metal nanoparticle aerogels. SEM and EDS results indicated that a loading of 59, 67, 39, and 46 wt % of Pd, Pt, Ni, and Sn nanoparticles was achieved. Pd/rGO aerogels of different Pd nanoparticle concentrations were exposed to H₂ gas to monitor the resistance change of the composites. The results suggest that rGO aerogels can achieve a higher nanoparticle loading by using chelation to minimize electrostatic interactions between metal ions and GO. Higher loading of Pd nanoparticles in graphene aerogels lead to improved hydrogen gas sensing performance.