Blood Protein as a Sustainable Bifunctional Catalyst for Reversible Li-CO2 Batteries

Electrochemical Li-CO2 cells, which provide a sustainable and environmentally friendly pathway away from greenhouse gases, often suffer from sluggish kinetics for the growth and evolution of the cathode species on an electrode. The problematic irreversibility of the solid-to-gas conversion reactions can be addressed by the introduction of efficient catalysts into the Li-CO2 cell. Here, we report the direct utilization of hemoglobin proteins, which are plentiful bioresources extracted from blood wastes, to effectively boost two-way Li-CO2 reactions. The hemoglobin was immobilized on a cathodic electrode and showed excellent catalytic activity and improved capacity for CO2 reduction and evolution reactions with a desirable weight ratio between the conductive carbons and the hemoglobin catalysts. We also verified the structural characteristics of lithium carbonate product species and the reversibility of the Li-CO2 reaction by ex situ studies. The iron ion active site in a heterocyclic porphyrin ring of hemoglobin can participate in the Li-CO2 reaction as a redox component.