Understand the local chemical environment of bioelectrocatalysis

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Importance

Enzymatic bioelectrochemistry concerns the integration of oxidoreductase enzymes into electrodes to allow and study the transfer of electrons between the surface of the material in the solid state and the biological catalyst. To achieve higher enzyme loading, and hence higher current densities, large-area strategies have been used to immobilize enzymes, but these porous electrode architectures amplify the formation of local chemical gradients. Selectivity and enzyme activity are highly dependent on these changes in the local environment, such as substrate concentration, pH, and concentration of electrolyte species. Here, electrochemical and computational techniques are applied to explore, and therefore optimize, the local environment of fuel-producing oxidoreductases, hydrogenase and formate dehydrogenase, in porous electrodes.

Summary

Bioelectrochemistry uses a combination of high surface area meso and macroporous electrode architectures to increase protein charge and electrochemical current response. While the local chemical environment has been studied in small molecule and heterogeneous electrocatalysis, the conditions for enzymatic electrochemistry are still commonly established based on analyzes of bulk solutions, disregarding conditions of non- equilibrium of the confined space of the electrodes. Here, we apply electrochemical and computational techniques to explore the local environment of fuel-producing oxidoreductases in porous electrode architectures. This better understanding of the local environment allowed simple manipulation of the electrolyte solution by adjusting the overall pH and pK of the buffer.a to achieve an optimal local pH for maximum activity of the immobilized enzyme. When applied to macroporous reverse opal electrodes, the advantages of higher charge and increased mass transport were utilized and as a result the electrolyte was adjusted to -8.0 mA⋅ cm−2 for the H2 evolution reaction and −3.6 mA ⋅ cm−2 for CO2 reduction reaction (CO2RR), demonstrating an 18-fold improvement on previously reported enzymatic CO2RR systems. This research highlights the critical importance of understanding the confined enzymatic chemical environment, thereby expanding the known capabilities of enzymatic bioelectrocatalysis. These considerations and insights can be directly applied to both bio(photo)electrochemical fuel and chemical synthesis, as well as enzyme fuel cells, to greatly improve fundamental understanding of the enzyme-electrode interface as well as performance. of the device.

Footnotes

    • Accepted November 16, 2021.
  • Author contributions: research designed by EEM and ER; EEM carried out experimental research; SJC performed computer modeling; AMC, ARO, and IACP provided enzymes and performed in-solution studies; EEM, SJC and ER analyzed the data; and EEM and ER wrote the article.

  • The authors declare no competing interests.

  • This article is a direct PNAS submission. NP is a guest editor invited by the Editorial Board.

  • This article contains additional information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2114097119/-/DCSupplemental.

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