Addition/Correction www.acsami.org
Correction to “A Smorgasbord of Carbon: Electrochemical Analysis of Cobalt−Bis(benzenedithiolate) Complex Adsorption and Electrocatalytic Activity on Diverse Graphitic Supports” Shawn C. Eady, Molly M. MacInnes, and Nicolai Lehnert* ACS Appl. Mater. Interfaces 2016, 8 (36), 23624−23634. DOI: 10.1021/acsami.6b05159 UV−visible spectroscopy and CV integration, which are 1.20 × 10−8 and 6.28 × 10−9 mol, respectively. To ensure that the difference in catalyst loading on graphite powder from these estimation methods is genuine, we repeated the experiment with a new batch of graphite from the same supplier. Using UV−vis titration and CV integration gave catalyst loadings (using 3 mg graphite powder) of 3.05 × 10−8 and 5.11 × 10−9 mol, respectively, which is in good agreement with the previous experiment. This result again confirms a significant difference in loading estimates by these two methods. Similar observations have previously been reported by Roberts and co-workers, who estimated loadings for nickel bis(diphosphine) dihydrogen production catalysts covalently bound to a glassy carbon electrode. Here, the catalyst loading estimates by CV provide a value an order of magnitude lower
A
n error in baseline subtraction used for the integration of the cyclic voltammetry (CV) data was discovered and corrected, increasing the catalyst coverage on the bulk graphite electrode (Figure 1) from 1.13 × 10−9 mol to 4.52 × 10−9 mol, and decreasing the estimated loading in GPEN films from 7.03 × 10−9 mol to 6.28 × 10−9 mol. The resulting areanormalized catalyst loadings for bulk graphite and GPEN films are determined to be 1.41 × 10−8 mol/cm2 and 1.96 × 10−8 mol/cm2, respectively. As a result of these changes in catalyst surface coverage (Γ), a corresponding change in estimated catalytic rate (kobs) is calculated with eq 1, as well as a change in turnover frequencies (TOF) and turnover number (TON) determined from bulk electrolysis (BE) studies results.1 kobs =
icat nFA Γ
(1)
Table 1. Previously Listed and Corrected Values Describing the Dihydrogen Evolution Catalytic Performance of Graphite-Adsorbed Cobalt Dithiolene Complexes
For the bulk graphite-deposited catalyst, the estimated kobs is calculated to change from 33 s−1 to 8.3 s−1. The average TOF and TON from electrolysis change from 30 s−1 and 8.71 × 105 in 8 h to 7.5 s−1 and 2.18 × 105 in the same time period. For the GPEN films, a change in kobs from 3.1 s−1 to 3.3 s−1 is observed. New average TOF and TON values of 4.4 s−1 and 1.11 × 105 are calculated from the electrolysis data for GPEN electrodes in place of the previously calculated values of 3.9 s−1 and 9.87 × 104. It is worth noting that these changes do not alter the agreement between kobs values obtained from eq 1 and the average TOF results calculated from bulk electrolysis studies, as shown in Table 1. The changes also do not significantly alter the difference in catalyst loading calculated by
bulk graphite previous loading (mol) loading (mol/cm2) icat (pH 1.5, mA) Kobs (s−1) initial TOF (s−1) average TOF (s−1) TON (time)
1.13 3.53 7 33 96 30 8.71 (8
−9
× 10 × 10−9
× 105 h)
GPEN on glassy carbon
corrected 4.52 1.41 7 8.3 24 7.5 2.18 (8
−9
× 10 × 10−8
× 105 h)
previous 7.03 2.10 4 3.1 7.4 3.9 9.87 (7
−9
× 10 × 10−8
× 104 h)
corrected 6.28 1.96 4 3.3 8.3 4.4 1.11 (7
× 10−9 × 10−8
× 105 h)
Figure 1. Baseline-corrected cyclic voltammogram (left) and integration (right) used for estimating catalyst surface coverage on bulk graphite electrodes. Cyclic voltammograms were generally run at 50 mV/s.
© XXXX American Chemical Society
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DOI: 10.1021/acsami.7b04549 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
ACS Applied Materials & Interfaces
Addition/Correction
than that obtained from X-ray photoelectron spectroscopy of the electrode surfaces.1 The most likely explanation for this finding is that not all of the catalyst present on the surface is electrochemically active.
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REFERENCES
(1) Das, A. K.; Engelhard, M. H.; Bullock, R. M.; Roberts, J. A. S. A Hydrogen-Evolving Ni(P2N2)2 Electrocatalyst Covalently Attached to a Glassy Carbon Electrode: Preparation, Characterization, and Catalysis. Comparisons with the Homogeneous Analogue. Inorg. Chem. 2014, 53, 6875−6885.
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DOI: 10.1021/acsami.7b04549 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
