Rotating Disk Electrode – Online Electrochemical Mass Spectrometry for Oxygen Reduction Reaction on Pt Electrode Surfaces

Abstract

Potential-dependent molecular behavior of dissolved O2 in the vicinity of a polycrystalline Pt electrode surface was studied in O2-saturated 0.1 M HClO4 solution using a newly developed online electrochemical mass spectrometry (OLEMS) with rotating disk electrode (RDE) method (RDE-OLEMS). A gas sampling tip was positioned at ~50 μm from the electrode surface; O2 concentration in the vicinity of the Pt electrode at open circuit potential (~0.8 V vs. RHE) depended on the disk rotation rates, and linear sweep voltammetry (LSV) of the Pt electrode showed diffusion-limiting currents in the RDE-OLEMS layout. Furthermore, simultaneously recorded RDE-OLEMS data for the potential-dependent O2 concentration were consistent with the LSV data recorded for a negative-going sweep. We have successfully applied the newly developed RDE-OLEMS method and it is effective for in-situ analysis of gaseous electrochemical reaction products and dissolved molecules in the vicinity of the electrode under electrochemical conditions.

Online Electrochemical Mass Spectrometry Combined with the Rotating Disk Electrode Method for Direct Observations of Potential-Dependent Molecular Behaviors in the Electrode Surface Vicinity

“…The potential sweep direction, disk rotation rate, and potential scan rate were tuned considering the above-mentioned retardation times of the O 2 ion signal measured by the Q-mass. 40 As can be seen in (c), the Q-mass ion currents of O 2 (MS-LSV) correspond well with the ORR currents (LSV), demonstrating that the potential-dependent behaviors of the dissolved O 2 present near the electrode surface can certainly be monitored by the RDE-OLEMS.…”

“…Probably, the conductance is low against the pumping speed of the used turbo-molecular pump (67 l min −1 ), resulting in retardation of the Q-mass detection. 40 Figure 2b shows LSV curves of the Pt electrode surface recorded for a positive-potential sweep from 0.05 to 1.05 V at a scan rate of 10 mV s −1 by the RDE-OLEMS setup, where the PEEK-made tip is located at ∼50 μm from the working disk electrode surface (Pt). The diffusion-limiting current regions for ORR from 0.2 to 0.6 V can be seen for all the LSVs.…”

“…, where the our homemade OLEMS setup [38][39][40] that previously constructed by referring the pioneering work by Wonders et al 31 is combined with a conventional RDE apparatus. As shown in Fig.…”

“…Therefore, in this study, we newly developed RDE-OLEMS to investigate potential-dependent molecular behaviors for both reactant and product molecules under the mass-transport-controlled conditions. The developed RDE-OLEMS, i.e., the homemade OLEMS setup [38][39][40] combined with a conventional RDE apparatus, was applied for the reactant molecule of O 2 for ORR on the Pt electrode and the product molecule of CO by ECR on the Au electrode. The results obtained by the RDE-OLEMS clearly demonstrate that electrode potential-dependent molecular behaviors can be monitored not only for reactant molecules but also for product molecules under the mass transport-controlled conditions and that z E-mail: naoto.todoroki.b1@tohoku.ac.jp the RDE-OLEMS is a novel, quite powerful tool for investigating electrocatalysis.…”