A successful
market introduction of electrocatalytically produced
hydrogen peroxide (H2O2) requires catalysts
that are highly selective, active, and economically suitable. Here,
we present important insights into tuning the selectivity toward H2O2 and elaborate on the opportunities opened for
high catalytic performance. Especially the metal loading, the accompanied
interparticle distance, and catalyst–support interaction were
identified as key contributors for high selectivity and activity.
We focused on the design of model catalysts with different Pd loadings
and distinct interparticle distances and their dependency on the selectivity
toward H2O2. The gained understandings can be
used as guidelines for the development of highly active and selective
catalysts while simultaneously reducing the noble metal loading and
the associated costs.
The oxygen reduction reaction (ORR) is typically slow. Its kinetics, however, are influenced not only by the structure, nature, and doping of electrocatalysts, but also by the loadings of these materials, where all of these factors influence ORR selectivity to produce H2O and/or H2O2. The loadings employed for graphene nanoribbon (GNR)‐modified glassy carbon (GC) electrodes and GC disk modified with commercial Pt (20 wt.%) on carbon (PtC) at 150 μg cm−2 (also resulting in electrode roughness) produced turbulence in the electrolyte flow, significantly changing the geometry of the rotating ring‐disk electrode (RRDE) and collection efficiency (N), as well as causing N to change with the rotation rate of the electrode. This effect toward the ORR was investigated with two analytical methods derived by Wu et al. and Zhou et al. A current deconvolution method for a better‐resolved Tafel analysis separating normalHnormalO2-
formation and reduction reactions resulted in more insightful understanding of the ORR responses provided by the RRDE for different GNR and PtC loadings.
Abstract:The aim of this study is to compare the electrochemical behaviour of graphene-based materials of different origin, e.g., commercially available graphene nanosheets from two producers and reduced graphene oxide (rGO) towards the oxygen reduction reaction (ORR) using linear sweep voltammetry, rotating disc electrode and rotating ring-disc electrode methods. We also investigate the effect of catalyst ink preparation using two different solvents (2-propanol containing OH´ionomer or N,N-dimethylformamide) on the ORR. The graphene-based materials are characterised by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Clearly, the catalytic effect depends on the origin of graphene material and, interestingly, the electrocatalytic activity of the catalyst material for ORR is lower when using the OH´ionomer in electrode modification. The graphene electrodes fabricated with commercial graphene show better ORR performance than rGO in alkaline solution.
There has been a
huge debate in the literature over the past few
years regarding the groups (C, O, and N groups and their quantities)
involved in oxygen reduction reaction on metal-free carbonaceous nanostructured
surfaces. The present study shows that the electrochemical stabilization
of graphene oxide nanoribbons (GONRs) leads to an increase in the
number of quinone groups on the surface of GONR electrodes. These
quinone groups are responsible for the high production of HO2
–. The percentage decrease observed in HO2
– production (in a region of defined potential)
is attributed to the presence of pyrrolic-N groups along with epoxy
groups on the electrochemically stabilized surface of graphene nanoribbon
(GNR) electrodes. The presence of pyrrolic-N groups along with epoxy
groups on the electrochemically stabilized surface of GNR electrodes
is observed concomitantly with a decrease in the amount of pyridinic-N
groups oxidized to N oxides from pyridinic-N groups in addition to
a significant decrease in the percent concentration of quinone groups.
The combination of pyrrolic-N groups (without ruling out the contribution
of pyridinic-N groups, which presented very low percentage content
with a total N atomic concentration of only 0.7%) with quinone groups
on a nonelectrochemically stabilized GNR surface is responsible for
the high production of HO2
–.
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