Influence of conductive carbon and MnCo2O4 on morphological and electrical properties of hydrogels for electrochemical energy conversion

Abstract

In this work, a strategy for one-stage synthesis of polymer composites based on PNIPAAm hydrogel was presented. Both conductive particles in the form of conductive carbon black (cCB) and MnCo₂O₄ (MCO) spinel particles were suspended in the three-dimensional structure of the hydrogel. The MCO particles in the resulting hydrogel composite acted as an electrocatalyst in the oxygen evolution reaction. Morphological studies confirmed that the added particles were incorporated and, in the case of a higher concentration of cCB particles, also bound to the surface of the structure of the hydrogel matrix. The produced composite materials were tested in terms of their electrical properties, showing that an increase in the concentration of conductive particles in the hydrogel structure translates into a lowering of the impedance modulus and an increase in the double-layer capacitance of the electrode. This, in turn, resulted in a higher catalytic activity of the electrode in the oxygen evolution reaction. The use of a hydrogel as a matrix to suspend the catalyst particles, and thus increase their availability through the electrolyte, seems to be an interesting and promising application approach.

Keywords: electrical properties; energy; hydrogel; hydrogen; oxygen evolution reaction; polymer composites.

Figure 1

SEM micrographs of freeze-dried nanostructures of pure (a, d) and composite hydrogel samples: Hgel-MCO-cCB 1:3 (b, e) and Hgel-MCO-cCB 1:6 (c, f).

Figure 2

EDS analysis of hydrogel composites: Hgel-MCO (a, d, g), Hgel-MCO-cCB 1:3 (b, e, h), Hgel-MCO-cCB 1:6 (c, f, i).

Figure 3

Transmittance plot in the function of wavenumber based on absorbance data from FTIR-ATR spectra of hydrogel composites and their components (a). FTIR graph of MnCo₂O₄ strongest characteristic transmittance peaks (b). Comparison of the intensity of P(NIPAAm) strongest characteristic transmittance peaks with different conductive carbon black concentrations in hydrogel composite samples (c).

Figure 4

Analysis of electrical properties of hydrogel-based samples with catalyst (M CO) and conductive (cCB) particles (experimental data (dot line) and Randles model results (solid line)): a) Bode modulus and b) phase angle with fitting curves, and c) Nyquist plots of hydrogel samples. d) Dependence of the hydrogel |Z| on the cCB concentration at 0.01 Hz.

Figure 5

Catalytic activity in the OER process of MCO particles dispersed in the hydrogel: a) polarisation curves, b) double-layer capacitance (C_dl), c) Tafel plots.

Figure 6

Scheme of hydrogel polymerisation process with electrocatalyst and conductive carbon particles.

Figure 7

System for measuring electrical properties of hydrogel-based samples with catalyst (MCO) and conductive carbon black (cCB) particles.