Summary This study demonstrated the capability of a novel method in controlling the structural and electrochemical properties of electrocatalysts, utilizing a pulsed‐ultraviolet (UV) setup for the synthesis procedure. A hand‐made reactor provided a new set of parameters. The variation of UVon and UVoff periods resulted in samples with a range of different structures, compositions, and activities. Graphene/Pt was prepared with varying forms of illumination pulse, and its hydrogen oxidation and oxygen reduction reaction performances were evaluated. Controlling the reduction degree of Pt ions on partially reduced graphene oxide was achieved by manipulating the setup design. The results revealed a dominant growth and agglomeration phase of Pt particles, mostly with metallic states, by increasing both UVon and Uoff time spontaneously. Long UVon without adequate UVoff did not result in promising electrocatalytic activities. In other words, different structures, compositions, and activities of samples suggested that not just the illumination is the crucial factor, it is also the resting time or UVoff which determines the surface adsorption kinetics, nucleation sites, and growth mechanism of nanoparticles. Further chemical reduction by highly concentrated ascorbic acid was used to confirm the proposed mechanisms, which lead to samples even with more metallic Pt (Pt0).

This study focuses on photocatalytic syntheses, in which transition metal ions (Co2+, Fe2+, or Ni2+), as the hole scavengers and surface modifiers of partially reduced graphene oxide, PRGO, were utilized to photoreduce Pt4+. A pulsed UV reactor was used to illuminate the precursors. The electrostatic interaction between the metal ions (Co2+, Fe2+, or Ni2+) and the oxygen functional groups on PRGO was the main parameter, proposed to be the reason controlling Pt4+ reduction and Pt structure and activity. The alternative assumption in managing the oxidation states of Pt was the variation in the oxidation rates of hole scavengers. Pt electrocatalysts’ structural and electrochemical characteristics revealed that utilizing the cobalt-based hole scavenger caused a dominant growth phase of Pt particles at preferred positions on PRGO, with metallic states and improved electrocatalytic activities (ECSA value of 191 m2·g–1 for Co2+ vs 141 m2·g–1 and 127 m2·g–1 for Fe2+ and Ni2+, respectively). Density functional theory (DFT) calculation, on the other hand, suggested that the greater affinity of cobalt and iron ions to oxygen groups could detach more “O” from the graphene plane. Based on the DFT results, less “O” groups in the vicinity of Pt particles gave an amorphous morphology to Pt and facilitated the hydrogen oxidation reaction (HOR).

The study of electrode processes at carbon electrodes has great relevance to a variety of electrochemical applications. The wide range of carbon materials, their possible combination, the variability of electrode design and fabrication techniques, the specific application purposes, all these elements show the richness and complexity of this research area in electrochemistry. In particular, Activated Carbon (AC) electrodes are widely used for charge storage in supercapacitors and capacitive deionization cells. For their porous structure and surface characteristics, this class of electrodes may pose serious challenges to the capacity of routine electrochemical methods to achieve an in-depth analysis and the deconvolution of different electrode processes. A relatively new and interesting method, the Step Potential Electrochemical Spectroscopy (SPECS), has been shown to be an effective way to separate the contributions of faradaic and non-faradaic processes to the total current at AC electrodes1. The technique consists in applying to the working electrode (WE) a series of small potential steps and recording the current decay during a time interval long enough to allow for equilibration. Relatively simple models are fitted to the transients, to derive parameters of capacitive charging and faradaic processes. In the present work, we explore further the capability of SPECS to characterize electrode processes at AC electrodes, having in mind two objectives in particular: the determination of the Potential of Zero Charge (EPZC ) and the separation and possible identification of faradaic processes, through a closer examination of experimental data.AC (YEC-8A) paste electrodes (80% AC, 10% carbon black and 10% PTFE) on graphite current collector (130 μm thick foil) were used as WE in 0.1 M NaClaq electrolyte. The EPZC was determined as the minimum of differential capacitance vs. potential plot (single-frequency EIS measurement at 5 mHz). SPECS was performed over the potential window from –0.25 to 0.75 VSCE both in the anodic and cathodic direction, using a step of 25 mV and equilibration time of 300 s (sampling time 0.1 s). SPECS current transients are simulated by a two-exponential decay function with a residual current.Normalized differential capacitance curves from EIS and SPECS are shown in Figure 1a. The value of EPZC is found at about 0.175 and 0.190 VSCE by EIS and SPECS, respectively. Additionally, a good agreement is found between the absolute capacitance minimum determined by either technique at electrolyte concentration from 0.01 to 1.0 M, see inset of Figure 1a. The plot of residual currents vs. potential from the analysis of SPECS data is shown in Figure 1b. The trend of the currents, in both scan directions, highlights two “inversion” potentials: at about 0 VSCE, during forward polarization, and at about 0.57 VSCE, during backward polarization; in other words, the residual current is positive on the anodic side and negative on the cathodic side vs. the inversion potential, thus recreating the typical shape...