No abstract

Here, we detail how the catalytic behavior of immobilized molecular electrocatalysts for the CO 2 reduction reaction (CO 2 RR) can be impacted by catalyst aggregation. Operando Raman spectroscopy was used to study the CO 2 RR mediated by a layer of cobalt phthalocyanine (CoPc) immobilized on the cathode of an electrochemical flow reactor. We demonstrate that during electrolysis, the oxidation state of CoPc in the catalyst layer is dependent upon the degree of catalyst aggregation. Our data indicate that immobilized molecular catalysts must be dispersed on conductive supports to mitigate the formation of aggregates and produce meaningful performance data. We leveraged insights from this mechanistic study to engineer an improved CO-forming immobilized molecular catalyst�cobalt octaethoxyphthalocyanine (EtO 8 −CoPc)�that exhibited high selectivity (FE CO ≥ 95%), high partial current density (J CO ≥ 300 mA/cm 2 ), and high durability (ΔFE CO < 0.1%/h at 150 mA/cm 2 ) in a flow cell. This work demonstrates how to accurately identify CO 2 RR active species of molecular catalysts using operando Raman spectroscopy and how to use this information to implement improved molecular electrocatalysts into flow cells. This work also shows that the active site of CoPc during CO 2 RR catalysis in a flow cell is the metal center.

A first-row metal phthalocyanine series is synthesized and the effects of axial metal-ligand substitution is investigated electrochemically and in the context of charge carriers for redox-flow batteries.

Here, we quantify the effect of an external magnetic field (β) on the oxygen evolution reaction (OER) for a cobalt oxide|fluorine-doped tin oxide coated glass (CoO x |FTO) anode. A bespoke apparatus enables us to precisely determine the relationship between magnetic flux density (β) and OER activity at the surface of a CoO x |FTO anode. The apparatus includes a strong NdFeB magnet (β max = 450 ± 1 mT) capable of producing a magnetic field of 371 ± 1 mT at the surface of the anode. The distance between the magnet and the anode surface is controlled by a linear actuator, enabling submillimeter distance positioning of the magnet relative to the anode surface. We couple this apparatus with a finite element analysis magnetic model that was validated by Hall probe measurements to determine the value of β at the anode surface. At the largest tested magnetic field strength of β = 371 ± 1 mT, a 4.7% increase in current at 1.5 V vs the normal hydrogen electrode (NHE) and a change in the Tafel slope of 14.5 mV/dec were observed. We demonstrate through a series of OER measurements at sequential values of β that the enhancement consists of two distinct regions. The possible use of this effect to improve the energy efficiency of commercial water electrolyzers is discussed, and major challenges pertaining to the accurate measurement of the phenomenon are demonstrated.

The synthesis and characterization of a new phthalocyanine (Pc) Mn-nitride complex, ( OEt Pc)MnN (2; OEt Pc = 1,4,8,11,15,18,22,, as well as its stable, readily accessible oxidized (2 + and 2 2+ ) and reduced (2 -, 2 2-) congeners is reported. This unique isostructural series displays switchable aromatic character spanning the aromatic (2), non-aromatic (2 2+ ), and antiaromatic (2 2-) triad, in addition to the open-shell radical states (2 + , 2 -). All complexes were structurally characterized and displayed significant structural distortions at the redox extrema (2 2+ , 2 2-) consistent with proposed [16 or 18]annulene  ring circuit models. Spectroscopic and computational studies further support these models. This isolated, fully characterized, isostructural series spanning five redox states (2 2+ , 2 + , 2, 2 -, 2 2-) is unique in both the Pc and related macrocyclic (ex. porphyrinoids) literature and may offer direct insight into structural-electronic correlations driven by switchable aromaticity.