Heterogenous Preparations of Solution-Processable Cobalt Phthalocyanines for Carbon Dioxide Reduction Electrocatalysis

Abstract

The development and implementation of technology that can capture and transform carbon dioxide (CO2) is of ongoing interest. To that end, the integration of molecular electrocatalysts into devices is appealing because of the desirable features of molecules, such as the ability to modify active sites. Here, we explore how the identity of the aliphatic group in 1,4,8,11,15,18,22,25-octaalkoxyphthalocyanine cobalt(II) affects the catalytic behavior for heterogeneous CO2 reduction electrocatalysis. The alkyl R-groups correspond to n-butoxy, sec-butoxy, and 2-ethylhexoxy. All of the catalysts are soluble in organic solvents and are readily solution-processed. However, the larger 2-ethylhexoxy group showed solution aggregation behavior at concentrations ≥1 mM, and it was, in general, an inferior catalyst. The other two catalysts show comparable maximum currents, but the octa sec-butoxy-bearing catalyst showed larger CO2 reduction rate constants based on foot-of-the-wave analyses. This behavior is hypothesized to be due to the ability of the sec-butoxy groups to eliminate the ability of the alkoxy oxygen to block Co Sites via ligation. CO2 reduction activity is rationalized based on solid-state structures. Cobalt(II) phthalocyanine and its derivatives are known to be good CO2 reduction catalysts, but the results from this work suggest that straightforward incorporation of bulky groups can improve the processability and per site activity by discouraging aggregation.

Inducing ring distortions in unsubstituted metallophthalocyanines using axial N-heterocyclic carbenes

“…For dome-type distortions the average of the absolute values and average of the actual values should be approximately equal. Applying these structural metrics to the five-coordinate PcM (NHC) complexes herein, isoindole torsion angle ranges of −3.1(4) to 4.3(4), −6.3(4) to 7.2(4), and −4.5(3) to 3.0(3)°, N meso torsion angles of 6.55(6), 0.41 (7), and 3.74(5)°, average N-isoindole torsion angles of 0(5), 1(3), and 2(2)°, and averages of the absolute values of the N-isoindole torsion angles of 4(3), 2(2), and 2(1)°for PcCo II (DIP), PcZn II (DIP), and PcZn II (DMB), respectively (Fig. 4), were identified.…”

“…Phthalocyanines (PcH 2 ) have a diverse coordination chemistry and are used in applications ranging from colourants to electrocatalysts. [1][2][3][4][5][6][7][8] The simplest complexes are those of ringunsubstituted PcH 2 , for which many metal-substituted PcM congeners that span the periodic table are known. However, the extended π system, and the resultant rigid, planar structure of unsubstituted PcM complexes result in a strong tendency for them to aggregate.…”

Electrocatalytic and Photoelectrocatalytic Sensors Based on Organic, Inorganic, and Hybrid Materials: A Review

“…To become a semiconductor, the two hydrogen atoms occupying the central ring can be replaced by a metal ion. The great stability in the redox processes of phthalocyanines attracts interest in using them in electrocatalysis processes [145][146][147][148][149][150][151]. Materials based on transition metal phthalocyanine have been extensively studied for the improvement of reactions involving oxygen (ORR and OER).…”

“…Materials based on transition metal phthalocyanine have been extensively studied for the improvement of reactions involving oxygen (ORR and OER). Tajbakhsh, E., et al used cobalt phthalocyanines in reducing carbon dioxide [146]. Eyele-Mezui, S. et al used phthalocyanine tetrasulfonate intercalated in metal-layered simple hydroxides (metal: Co, Cu, and Zn) in the evaluation of the electrocatalytic activity, with a focus on fuel cells, where the materials showed potential [145].…”

Contemporary Strategies for Immobilizing Metallophthalocyanines for Electrochemical Transformations of Carbon Dioxide

“…In work from our group, we explored the relationship between the degree of aggregation and the type of substitution at the α position [56]. In simple drop-cast preparations of 6-8 (Figure 5), we demonstrated that bulkier alkoxy-chains do not necessarily lead to better dispersion and, therefore, more facile access to active sites.…”