Conducting Copper(I/II)-Metallopolymer for the Electrocatalytic Oxygen Reduction Reaction (ORR) with High Kinetic Current Density

Abstract

The oxygen reduction reaction (ORR) is still the most research-intensive aspect of a fuel cell. The sluggish kinetics of the electrocatalysts toward the ORR requires large amounts of platinum to be used as cathode material, which calls for alternatives to replace or minimize the amount of the noble metals used. This study describes the synthesis and complete characterization of a copper metallopolymer (Cu MP) based on a conducting polymer (CP) and single-site catalytic centers for the electrocatalytic ORR. The copper (II) catalyst, embedded in a redox-active and conducting polymeric environment, was pursued as a potential candidate to replace noble metals in fuel cell applications. Performance studies at a rotating disk electrode (RDE) showed that the metallopolymer exhibited a direct four-electron reduction at potentials between −150 and −350 mV vs. the reversible hydrogen electrode (RHE) and high kinetic current densities of over 22.62 mA/cm2. The kinetic current densities obtained at the Cu MP electrode outperformed most of the reported state-of-the art electrocatalysts toward the ORR. Further analysis of the Cu/CP hybrid revealed the copper being largely reduced to the oxidation state +I.

Copper Metallopolymer Catalyst for the Electrocatalytic Hydrogen Evolution Reaction (HER)

“…Using copper (Cu), the metallopolymer revealed activities for the electrocatalytic hydrogen evolution reaction (HER) at overpotentials comparable to a platinum electrode in a phosphate buffered buffer saline solution (PBS) and at neutral pH 7.4. However, in opposition to the previously reported Cu metallopolymer (Cu MP) with a redox-active hydroquinone/benzoquinone pendant unit [22], the current Cu MP did not show any significant activity towards the oxygen reduction reaction (ORR). To the best of our knowledge, this is the first Cu PHAM electrode material showing activities toward HER at overpotentials close to a Pt electrode and at neutral pH.…”

“…Copper is known to be partly reduced by x-ray radiation under ambient conditions during the sample analysis [28] that can also be assisted by ligand effects. Nonetheless, the high content of Cu(I) follows the trend of the previously reported Cu metallopolymer with a redox-active moiety [22].…”

“…The S(2p) core-level spectra of the polymer P OS and its metal hybrid P OS [Cu] exhibited two distinct binding energies with different ratios in intensity indicating mixtures of thiophene and sulfone functional groups (Figure 3b), each [22,29,30]. In both materials, the fitted binding energies appeared with the typical S(2p) doublet with 2/1 ratio and 1.2 eV splitting [30].…”

Nanostructure Engineering of Metal–Organic Derived Frameworks: Cobalt Phosphide Embedded in Carbon Nanotubes as an Efficient ORR Catalyst

“…The electrochemical measurements were conducted in a three-electrode system, consisting of a working electrode (a glassy carbon rotating disk), a counter electrode (a graphitic carbon rod), and a reference electrode (vs. Ag/AgCl). The recorded working potentials vs. Ag|AgCl (3M KCl) were converted into the reversible hydrogen electrode (RHE) according to the equation E(RHE) = E (Ag|AgCl) + 0.059 pH + 0.210 V, where pH (0.1 M KCl) = 5.8 [42]. A catalyst loading of 0.3 mg cm −2 was deposited on the glassy carbon electrode surface (0.19625 cm 2 ).…”

The influence of copper ions on the transport and relaxation properties of hydrated eumelanin

“…In the literature, one can find many examples of the successful use of Cu ions for this purpose. [54][55][56] For example, the effect of Cu 2+ ions specifically on the EPR spectra of eumelanin was studied for the first time more than 50 years ago. 57 Then and in later studies, Cu 2+ ions reduced the EPR signal of the free radical of the material.…”