Fabrication and Characterization of Metal‐Free Composite Electrodes Based on Few‐Layer‐Graphene Nanoplatelets for Oxygen Reduction Reaction Applications

Abstract

Innovative technologies such as fuel and solar cells, supercapacitors, batteries, sensors, electrochemical energy storage devices are some of the most studied solutions to future energy demands due to an exponential population increase, estimated to reach over nine billion by 2050. [1] In fuel cells, chemical energy is directly converted to electricity. This fact is the main driving force through high-performance electrodes with improved catalytic activities toward hydrogen oxidation reaction (HOR) or oxygen reduction reaction (ORR). The final performance of a microbial fuel cell (MFC) will depend on the following parameters: 1) the power at the output, 2) the current density, and 3) the Coulombic efficiency, [1,2] which in turn depend on several factors such as the conductivity and porosity of the anode, the type of proton exchange membrane used to separate the cell chambers, the type of organic substrate used in the oxidation reaction at the anode, as well as the ORR at the cathode. However, the cathodic ORR in many cases has proven to be a limiting factor in the total energy generation in the cells, hence considered as one of the greatest performance indicators of a microbial fuel cell. [2] The commercial Pt/C catalyst is the common reference because of its great performance towards ORR with a limiting current density around 6 mA cm À2 at 0.7 V versus RHE (reversible hydrogen electrode) and 1600 rpm. Catalysts such as phosphorus doped hierarchical porous carbon showed a shift of around 70 mV for the onset potential compared with the Pt/C electrode. [3] Carbon fiber paper with Pt 3 Co showing a limiting current density of 25.8 mA cm À2 at 0.2 V versus RHE and 2500 rpm [4] and nanocomposites based on hybrid Mn 3 O 4 and oxidized graphene flakes provide a limiting current density of 2.8 mA cm À2 at À0.6 V and 1600 rpm. [5,6] Despite being the material with the highest electrocatalytic activity for ORR reported so far, Pt presents certain disadvantages like its high cost, toxicity, chemical instability, and biofouling, which still limit a widespread application. [7,8] These are the principal driving forces to find affordable materials to compete with Pt for ORR. Other metals such as copper, cobalt, or iron have been also reported as good candidates to replace the expensive Pt electrodes. Those materials exhibited currents, durability, and tolerance comparable with Pt, however, their ecological impact is highly

Recent advances in the modification of electrodes for trace metal analysis: a review

“…Five main types of NMs, i.e. , graphene, graphene oxide (GO) and reduced graphene oxide (rGO), 22–92 NPs, 23–25,27,31,56,57,59,64,67,70,83,86,87,93–138 single and multiwalled carbon nanotubes (SWCNTs and MWCNTs), 32,83,89,98,99,101,113,129,133,139–162 nanosheets, 34,85,107,111,139,162–166 and nanofibers, 167–169 have been employed in the modification of the electrodes used in the determination of heavy metals. Nanocubes, nanoflakes, nanospheres, and nanodiamonds 75,170–175 are among the other types of NMs used in the modification of the electrodes.…”

Nanofluid Formulations Based on Two-Dimensional Nanoparticles, Their Performance, and Potential Application as Water-Based Drilling Fluids

“… 28 − 30 At this scale, nanomaterials would exhibit totally different physicochemical properties, including improved electronic properties such as thermal and electrical conductivities, mechanical properties, high specific surface area, magnetism, quantum effects, and antimicrobial activity, among others, if compared with their macroscopic counterpart. 19 , 21 , 23 , 29 , 31 − 34 Most of the latter characteristic features are often absent in their macroscopic form, and they are closely related to their sizes and morphologies, which can vary from nanoparticles with well-defined geometry (spheres, triangles, squares, rhombuses, and plates), nanorods, nanotubes, nanosheets, etc. 28 , 29 , 35 Nanomaterials are classified as zero-dimensional such as nanoparticles, one-dimensional such as nanorods nanostructures, two-dimensional such as flat layer-like nanoparticles, and three-dimensional such as those nanostructures formed by the interaction of two or several nanoparticles.…”

“…Many attempts have been made to modulate the rheological, filtration, and heat transfer properties of DF formulations using nanoparticles as additives, viscosifiers, LCMs, or density regulators by exploiting nanotechnology. ,,,− The enhancement of their properties due to the inclusion of nanomaterials is attributed to their intrinsic properties at the nanoscale. In fact, nanomaterials formulation must ensure that at least one of their constituents possesses sizes up to 100 nm (1 nm = a billionth of a meter). − At this scale, nanomaterials would exhibit totally different physicochemical properties, including improved electronic properties such as thermal and electrical conductivities, mechanical properties, high specific surface area, magnetism, quantum effects, and antimicrobial activity, among others, if compared with their macroscopic counterpart. ,,,,− Most of the latter characteristic features are often absent in their macroscopic form, and they are closely related to their sizes and morphologies, which can vary from nanoparticles with well-defined geometry (spheres, triangles, squares, rhombuses, and plates), nanorods, nanotubes, nanosheets, etc. ,, Nanomaterials are classified as zero-dimensional such as nanoparticles, one-dimensional such as nanorods nanostructures, two-dimensional such as flat layer-like nanoparticles, and three-dimensional such as those nanostructures formed by the interaction of two or several nanoparticles. ,, Typical nanoparticles used so far in drilling mud formulations include but are not limited to carbonaceous nanostructures (carbon, buckminsterfullerene, carbon nanotubes, and graphene), − copper oxide (CuO), zinc oxide (ZnO), titanium dioxide (TiO 2 ), yttrium oxide (Y 2 O 3 ), ferric oxide (Fe 2 O 3 ), silicon dioxide (SiO 2 ), alumina (Al 2 O 3 ), bismuth ferrite, nanocellulose, nanoclays, and molybdenum disulfide (MoS 2 ). ,,,,,− The fabrication of high-performance hybrid muds based on the association of two or more of the preceding nanoparticles has also been reported. ,…”

Polyvinyl Alcohol Films Loaded with Silver Nanostructures with Different Sizes and Shapes with Tuneable Plasmonic and Electric Properties. A Spectroscopic Study

“…The combination of nanomaterials with a polymer matrix for the preparation of composite materials, called hybrids or nanocomposites 8 , allows modulating the properties of precursor materials to tailor them for specific applications. In particular, conductive polymer composites have a key role in the development of electronic devices such as flexible screens 9 and in the manufacture of electrochemical and flexible energy storage and conversion devices, among others 10,11 while maintaining synthetic feasability 12 and low production costs 13 .…”