The use of synthetic inorganic complexes as supported catalysts is a key route in energy production and in industrial synthesis. However, their intrinsic oxygen sensitivity is sometimes an issue. Some of us have recently demonstrated that hydrogenases, the fragile but very efficient biological catalysts of H2 oxidation, can be protected from O2 damage upon integration into a film of a specifically designed redox polymer. Catalytic oxidation of H2 produces electrons which reduce oxygen near the film/solution interface, thus providing a self-activated protection from oxygen [Plumeré et al., Nat Chem. 2014, 6, 822-827]. Here, we rationalize this protection mechanism by examining the time-dependent distribution of species in the hydrogenase/polymer film, using measured or estimated values of all relevant parameters and the numerical and analytical solutions of a realistic reaction-diffusion scheme. Our investigation sets the stage for optimizing the design of hydrogenase-polymer films, and for expanding this strategy to other fragile catalysts.
Microscale uniformity and long-range cohesion in multi-functional films assembled through drop-casting is realized by in situ gelation of monodisperse building blocks.
Energy
conversion schemes involving dihydrogen hold great potential
for meeting sustainable energy
needs, but widespread implementation cannot proceed without solutions
that mitigate the cost of rare metal catalysts and the O2 instability of biological and bioinspired replacements. Recently,
thick films (>100 μm) of redox polymers were shown to prevent
O2 catalyst damage but also resulted in unnecessary catalyst
load and mass transport limitations. Here we apply novel homogeneous
thin films (down to 3 μm) that provide protection from O2 while achieving highly efficient catalyst utilization. Our
empirical data are explained by modeling, demonstrating that resistance
to O2 inactivation can be obtained for nonlimiting periods
of time when the optimal thickness for catalyst utilization and current
generation is achieved, even when using highly fragile catalysts such
as the enzyme hydrogenase. We show that different protection mechanisms
operate depending on the matrix dimensions and the intrinsic catalyst
properties and can be integrated together synergistically to achieve
stable H2 oxidation currents in the presence of O2, potentially enabling a plethora of practical applications for bioinspired
catalysts under harsh oxidative conditions.
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