Integrated CO2 Capture and Conversion to Formate with a Molecular Platinum Bis(diphosphine) Electrocatalyst

TL;DR

A new platinum catalyst efficiently converts captured CO2 into formate, skipping energy-intensive concentration steps.

Contribution

A molecular platinum catalyst enables integrated CO2 capture and conversion with high efficiency.

Findings

The catalyst [Pt(dmpe)2](PF6)2 achieves >70% Faradaic efficiency in converting CO2 to formate.

Phenol facilitates CO2 release from the sorbent, enabling its electrochemical reduction.

Hydride transfer kinetics and mechanism were studied computationally and experimentally.

Abstract

Carbon dioxide is
a potentially valuable feedstock for carbon-based
fuels or commodities but is only available in dilute streams. Many
studies have focused on either the capture and concentration of CO2 or the reduction of pure CO2 streams. The direct
reduction of sorbent-captured CO2 in an integrated process
would skip the energy-intensive CO2 concentration and sorbent
regeneration step. Herein, we report the electrocatalytic reduction
of 1,3-bis­(2,6-diisopropylphenyl)­imidazolium-2-carboxylate (IPr·CO2), which forms quantitatively from the reaction of sorbent
1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene (IPr) with 10% and
0.04% CO2 streams, by catalyst [Pt­(dmpe)2]­(PF6)2 (dmpe = 1,2-bis­(dimethylphosphino)­ethane) to
formate with >70% Faradaic efficiencies. Unexpectedly, experimental
studies indicate that the proton source phenol facilitates rapid decarboxylation
of IPr·CO2 to release CO2, which is the
substrate for reduction. Kinetic studies determined the rate of hydride
transfer from a catalytic intermediate [HPt­(dmpe)2]­(PF6) to form the C–H bond in formate to be 0.22 M–1s–1. Further details on the mechanism,
transition state energy, and structure for hydride transfer to CO2, a common step in CO2 reduction, were explored
using computational methods.

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