# Peripheral Bromination for Strongly Affecting the Structural, Electronic, and Catalytic Properties of Cobalt Corroles

## TL;DR

This paper shows how adding bromine to a cobalt corrole significantly changes its structure and improves its ability to catalyze hydrogen production.

## Contribution

The study reveals a novel effect of bromide substituents on cobalt corroles, enhancing their catalytic performance for hydrogen evolution.

## Key findings

- Bromination causes a nonplanar macrocycle and alters the electronic spectrum of the cobalt corrole.
- The modified corrole catalyzes hydrogen evolution with a low onset potential of −0.96 V vs. Fc+/Fc.
- It achieves 97% Faradaic efficacy in hydrogen production from acidic water at low potentials.

## Abstract

The feasibility of a hydrogen-based economy critically
depends
on the development of catalysts for the hydrogen evolution reaction
(HER) that do not rely on Pt or other noble metals. Contemporary efforts
are focused on developing first-row transition metal complexes that
will be operative at low overpotentials and catalyze the reaction
with high efficacy and turnover rates. We now report a surprisingly
strong effect of bromide substituents on the structure, coordination
chemistry, electronic spectrum, reduction potentials, and catalytic
activity of an already electron-poor cobalt corrole. The six-coordinate
cobalt­(III) complex of the brominated corrole displays a very nonplanar
macrocycle, its axial pyridines are perpendicular to each other, the
maxima in the electronic spectrum are red-shifted by almost 70 nm,
and it is reduced by 600 mV less negative potentials. It catalyzes
the HER from an organic acid in an organic solvent with a very low
onset potential of −0.96 V vs. the Fc+/Fc couple
and has been used for the preparation of a catalyst-modified cathode
to produce hydrogen gas from acidic water with 97% Faradaic efficacy
at potentials as low as −0.4 V vs. RHE.