Electrochemical Activities of Mesoporous Pt Particles/MWCNT/ITO Electrodes for Hydrogen Generation and Glycerol Oxidation
Authors: Sugiyama Naoki , Matsunaga Mariko 
Published: December 2024

Hydrogen produced via water electrolysis has attracted attention as a next-generation secondary energy source because of its high mass energy density and its ability to be produced by low greenhouse gas emissions during water electrolysis. In contrast to hydrogen generation at the cathode in water electrolysis, oxygen production at the anode via water electrolysis, requires a high overpotential. In this study, glycerol oxidation, which produces fine chemicals, was used to reduce the overpotential of the anode reaction. Platinum is a highly active catalyst for both hydrogen production and glycerol oxidation; however, it is not suitable for large-scale operations because of its high cost. To reduce the amount of platinum used, mesoporous platinum was electrochemically deposited on multiwalled carbon nanotube (MWCNT) film electrodes,to prepare electrodes with excellent conductivity and a large Pt surface area. The three-dimensional structure of the porous composite thin-film influences the mass transfer of products associated with hydrogen production and glycerol oxidation. Furthermore, the morphology of mesoporous Pt can nfluence electrohemical activities for these reactions by changing the surface structure of platinum. In this study, we investigated the effects of potential and the amount of electricity applied during mesoporous Pt deposition, resulting in different Pt morphologies, on the electrochemical activities for hydrogen production and glycerol oxidation at thin-film electrodes.

MWCNTs were deposited on the ITO substrate via electrophoresis using sodium dodecyl benzene sulfonate (SDBS) as a surfactant. Subsequently, Pt particles were deposited on the MWCNT film electrodes via chronoamperometry in a solution containing Pt ion and Brij58. The Pt particles were deposited until the amount of electric charges reached 100 mC, 300 mC, 500 mC, and 800 mC by applying different potentials to the MWCNT film electrode, i.e., -0.1 V, -0.3 V, -0.5 V, or -0.7 V. Subsequently, micelles of Brij58 embedded in the Pt particles were removed by immersing the electrodes in ethanol to prepare mesoporous Pt/MWCNT electrodes with pore sizes in Pt particles of 5-10 nm. To evaluate the electrochemical performance of the as-prepared electrodes for hydrogen production and glycerol oxidation, cyclic voltammetry (CV) and polarization curve measurements were performed in a 0.1 M glycerol solution containing 0.1 M NaOH. All electrochemical measurements were carried out using a three-electrode cell with an as-prepared electrode as the working electrode, Ag/AgCl (saturated KCl) as the reference electrode, and platinum wire as the counter electrode.

As shown in Fig. 1 and 2, one main oxidation peak was observed in cyclic voltammograms measured in the glycerol solution for all mesoporous Pt particles/MWCNT electrodes at around 0.3 V, and additional oxidation peak was observed at nobler potential than the main peak when the amount of electric charge during platinum deposition was 300 mC and more for electrodes prepared at -0.1 V. These peaks are due to the oxidation current related to glycerol, as both of them were not observed in the 0.1 M NaOH solution. By increasing the electrical charges for Pt deposition, the oxidation peak potential at around 0.3 V was observed to shift to baser potential (Fig.1), which suggest better electrochemical activity. Comparing the voltammograms of electrodes prepared at different deposition potentials, the oxidation peak potential is the smallest for the electrode prepared at -0.3 V, and the oxidation peak current at around 0.3 V appeared to be larger when applying potential of -0.5 and -0.7 V (Fig.2). These changes both in the potential and current of the peak are partially due to the effect of the additional oxidation peak observed at nobler potential than the main peak, which was observed to shift to a baser potential by changing the deposition potential from -0.1 V to -0.7 V. The exchange current density calculated from the polarization curve was 4.64 mA/㎠ for hydrogen production and 9.12 mA/㎠ for glycerol oxidation for the Pt/MWCNT electrodes prepared at -0.5V with 300mC, showing the best electrochemical activity in both reactions among all the prepared-electrodes. The influence of the thin-film morphology is also discussed in this presentation.

Figure 1