Understanding the local chemical environment of bioelectrocatalysis

abstract

Bioelectrochemistry uses a range of high surface area meso- and macroporous electrode architectures to increase protein loading and electrochemical current response. While the local chemical environment has been studied in small molecule and heterogeneous electrocatalysis, the conditions in enzyme electrochemistry are still often set based on bulk solution assays without adequately considering the non-equilibrium constraints of the limited electrode space. Here we apply electrochemical and computational techniques to probe the local environment of fuel-producing oxidoreductases within porous electrode architectures. This improved understanding of the local environment allowed easy manipulation of the electrolyte solution by adjusting the pH and buffer pK_one to achieve an optimal local pH for maximum activity of the immobilized enzyme. Application to macroporous inverse opal electrodes took advantage of higher loading and increased mass transport, and consequently the electrolyte was adjusted to achieve −8.0 mA ⋅ cm⁻² for the h₂ evolutionary response and −3.6 mA ⋅ cm⁻² for the CO₂ Reduction reaction (CO₂RR), showing an 18-fold improvement over previously reported enzymatic CO₂RR systems. This research emphasizes the critical importance of understanding the limited enzymatic chemical environment, thereby expanding the known possibilities of enzyme bioelectrocatalysis. These considerations and insights can be directly applied to bio(photo)electrochemical fuels and chemical synthesis as well as to enzymatic fuel cells to greatly improve the fundamental understanding of the enzyme-electrode interface as well as device performance.