Suppressing hydrogen peroxide generation to achieve oxygen-insensitivity of a [NiFe] hydrogenase in redox active films

Huaiguang Li,Alaa A Oughli,Erik Freier,Nicolas Plumeré,Darren Buesen,Ute Münchberg,Wolfgang Lubitz

doi:10.1038/s41467-020-14673-7

Abstract

Redox-active films were proposed as protective matrices for preventing oxidative deactivation of oxygen-sensitive catalysts such as hydrogenases for their use in fuel cells. However, the theoretical models predict quasi-infinite protection from oxygen and the aerobic half-life for hydrogenase-catalyzed hydrogen oxidation within redox films lasts only about a day. Here, we employ operando confocal microscopy to elucidate the deactivation processes. The hydrogen peroxide generated from incomplete reduction of oxygen induces the decomposition of the redox matrix rather than deactivation of the biocatalyst. We show that efficient dismutation of hydrogen peroxide by iodide extends the aerobic half-life of the catalytic film containing an oxygen-sensitive [NiFe] hydrogenase to over one week, approaching the experimental anaerobic half-life. Altogether, our data support the theory that redox films make the hydrogenases immune against the direct deactivation by oxygen and highlight the importance of suppressing hydrogen peroxide production in order to reach complete protection from oxidative stress.

Highlights

Redox-active films were proposed as protective matrices for preventing oxidative deactivation of oxygen-sensitive catalysts such as hydrogenases for their use in fuel cells
In order to decipher the causality between H2O2 generation and the loss of functionality of viologen-modified matrices in aerobic conditions, we compare the behavior of the films in the presence and absence of a catalyst for H2O2 disproportionation
The discrepancy between model predictions and experimental observations for the half-life of O2-sensitive catalysts embedded in viologen-modified films used as protection matrices has been revealed through a combination of operando confocal fluorescence microscopy (CFM) and coherent anti-Stokes Raman scattering (CARS) coupled with electrochemistry

Summary

Introduction

Redox-active films were proposed as protective matrices for preventing oxidative deactivation of oxygen-sensitive catalysts such as hydrogenases for their use in fuel cells. Recent reports demonstrated the effective integration of enzymes such as hydrogenases[1,2,3,4], nitrogenase[5], formate dehydrogenase[6], and photosystems[7,8,9,10,11] as well as molecular catalysts[12,13,14] in redox matrices on electrode surfaces Since many of these catalysts are sensitive to O2 to the extent that they deactivate within seconds under aerobic conditions[15], the polymer films were further engineered as protection matrices to avoid oxidative deactivation[1,2,3,6,9,16]. The turnover stability in anaerobic experiments reaches weeks[1] This discrepancy between experiments and theoretical predictions implies that under aerobic conditions, processes other than O2-induced deactivation cause loss in catalytic current. Our data validate the predictions from our previous model[3,25] that protection within redox films make catalysts immune to O2, and demonstrate that suppression of reactive oxygen species is necessary to avoid oxidative degradation of the catalytic films

Methods

Results

Conclusion