Design and use of a flexible carbon wax electrode for electrochemical analyses and water splitting electrocatalysis
Creators: name: Lovander, Matthew Douglas
Publisher: name: University of Iowa
Year: 2024
Subjects: Capacitance
Carbon wax electrode
HER
OER
ORR
public abstract
Electrochemistry

description: Additives, such as binders or films, are commonly used to attach solids onto an electrode surface for electrochemical analyses. These additives can significantly alter the measured electrochemical behavior of the solids. An adequately conductive electrode that provides an adhesive and embeddable surface for solids is highly desirable to remove the use of additives and their undesirable effects. The work presented in this thesis describes the development of a working electrode with an embeddable surface for electrochemical analyses of dissolved species, and on solid electrocatalysts for applications including electrochemical water-splitting reactions namely, the hydrogen evolution reaction (HER), the oxygen evolution reaction (OER), and the oxygen reduction reaction (ORR). The Teflon housed carbon wax (Cwax) electrode is easily produced in-house, in large quantities, and unique surface enables particulate samples to be embedded onto the electrode surface without other adhesives.
description: The Cwax electrode tips consisted of a 45 wt% graphite to 55 wt% paraffin wax composition that was chosen based on previous literature. Once developed, the electrochemical performance of the Cwax electrodes was compared to commercially available glassy carbon electrodes (GCE). Similar to the GCEs, the Cwax electrodes present stable potential windows in several electrolytes. The stable performance of the Cwax electrodes led to the examination of a dissolved redox couple by both Cwax and GC electrodes. The Cwax electrodes provided similar electrochemical behavior to the GCE with slight increases in resistance due to the high percentage of nonconductive paraffin wax. The Cwax electrode resistance was later improved and tuned by follow-up research by other group members.
description: The respectable stability of the electrode behavior for the Cwax electrodes led to their use in several electrochemical experiments on a variety of metal phosphides, thiophosphates, and oxides synthesized in the Gillan group and detailed in this thesis. Prior to any advanced electrocatalytic work with research samples, several standard electrocatalysts, 10% Pt-C, 20% Pt-C, and RuO2, were tested with the Cwax electrodes. The 10% Pt-C catalyst is a standard reference catalyst for the HER in 0.5 M sulfuric acid, and in basic electrolytes, 0.1 M KOH, 20% Pt-C catalysts are referenced for ORR with rotating disk electrodes and RuO2 catalysts are standard for OER. The ~0 mV HER onset potential and the ~-50 mV potential for an HER current density of 10 mA cm-2 for the 10% Pt-C catalyst embedded on the Cwax electrode compared well with reported literature in 0.5 M sulfuric acid. The 20% Pt-C catalyzed ORR experiments in 0.1 M KOH did not perform as well to literature with only 3 calculated electrons transferred when 4 were expected, a possible reflection of the kinetics for this system between peroxide formation (n = 2) and oxygen reduction (n = 4) or possible difficulties with the rotation apparatus as work with the rotation apparatus is only in its initial proof-of-concept and design phase. The ~1.450 V OER onset potential for RuO2 embedded on a static Cwax electrode tip compared very well with reported onset potentials.
description: Metal phosphides (MPx), specifically CoP3, CuP2, FeP2, and NiP2, that were synthetically produced in the Gillan Laboratory by anion exchange reactions were systematically and extensively examined by electrochemical methods for HER electrocatalysis. All of the MPx materials showed some to significant HER activity, with an overall relative activity trend of CoP3 &gt; c-NiP2 &gt; m-NiP2 &gt; FeP2 &gt;&gt; CuP2. The activity of CoP3 stood out in both extended cycling and long term high current density demand experiments in both 0.5 M sulfuric acid and in a 1.0 M phosphate buffered solution. The CoP3 sample only required an HER onset potential of ~-30 mV and ~-150 mV potential for an HER current density of 10 mA cm-2 and the CoP3 sample maintained 98% stability at a constant applied potential of -170 mV for 18 hours that produced a near constant ~15 mA cm-2 current density. The electrochemically active surface area (ECSA) of each metal phosphide sample was determined by cyclic voltammetry and the CoP3 had the largest ECSA value (~20 cm2) and it maintained throughout all HER experiments. The copper phosphide (CuP2) sample displayed odd behavior, as the current density improved with cycling, which led to successful post electrochemical analyses with the carbon wax electrode tips by methods such as: SEM, XRD, and EDS.
description: Metal thiophosphates (MPS3) of Co, Fe, and Ni that were synthetically produced in the Gillan Laboratory by anion exchange reactions were electrochemically examined for HER electrocatalysis. The more anion rich thiophosphates () did not display HER electrocatalytic activities as high as those for the metal phosphides however, similar to the MPx samples, the cobalt containing catalyst was the most well behaved and best performing HER electrocatalyst in 0.5 M sulfuric acid, onset and 10 mA cm-2 current density potentials of ~-100 mV and ~-225 mV respectively.
description: Metal oxides (MyOx), Co3O4 and NiO, were produced on templated, chemically dehydrated leaves by the Gillan Laboratory. These metal oxides were preliminarily investigated as possible supercapacitance materials as well as oxygen evolution electrocatalysts, both in basic electrolytes. Initial results displayed low to moderate capacitance capabilities for all tested samples, with Co3O4 performing comparable to metal oxide nanoparticles. In addition, appreciable OER behavior was identified for some of the samples. The nickel oxide templated on the Jade leaves displayed the most promising OER activity with an applied potential of ~1.740 V for 10 mA cm-2 current density, only ~20 mV higher than the RuO2 standard.
description: Lastly, an Excel Visual Basic for Applications (VBA) program for quickly and systematically processing large data sets is presented. The program allows 100 datasets to be processed into Excel spreadsheets and charts in approximately 5 minutes compared to several hours. The analysis capabilities and automated electrochemical processing of larger data sets described in this thesis are a product of output from this VBA Excel macro program.