Investigating the Influence of Inorganic Cations on Electrocatalytic Activity and Stability of Pt Catalysts at Neutral pH

The chemical industry remains one of the largest contributors to global greenhouse gas emissions due to its heavy reliance on fossil fuels as both feedstock and energy source. As the intensifying climate crisis demands urgent action, decarbonizing chemical manufacturing has become a major focus to achieve net-zero emissions (NZE) targets. One promising pathway toward this goal is the electrification of chemical processes, which can replace fossil-fuel combustion with renewable electricity and enable energy-efficient, low-carbon transformations.

Concurrently, advances in synthetic biology are reshaping chemical manufacturing by enabling the use of renewable biomass instead of fossil-derived resources. Although metabolic engineering has made notable breakthroughs, achieving high-yield microbial production of every desired molecule remains challenging. Therefore, integrating biomanufacturing with catalytic upgrading offers significant potential, where microorganisms generate platform intermediates that are subsequently converted into commodity chemicals through catalysis. Electrocatalysis, in particular, provides a sustainable route by coupling catalytic transformations with renewable electricity.

Integrating these two approaches, hybrid microbial electrosynthesis (HMES) represents a promising strategy for low-carbon chemical production. In this process, engineered microorganisms ferment biomass into platform intermediates that can be directly converted into value-added products through electrocatalysis, using the fermentation broth directly as the reaction medium. However, fermentation broths present a chemically complex environment. Alongside biogenic impurities such as amino acids and peptides, dissolved electrolyte ions can alter catalytic behavior by modifying interfacial electric fields and solvation structure. While the influence of alkali cations such as Na⁺, K⁺, and Cs⁺ on electric double-layer properties has been studied under extreme pH conditions, their effects near neutral pH, which reflects most fermentation media, remain poorly understood.

This study investigates how electrolyte composition affects electrocatalytic performance under conditions representative of HMES. Specifically, we examine the role of fermentation-derived cations (Li⁺, Na⁺, K⁺, NH₄⁺, Mg²⁺, Mn²⁺) in modulating the activity and selectivity of platinum (Pt) catalysts at near-neutral pH for the hydrogen evolution reaction (HER) and the electrocatalytic hydrogenation (ECH) of cis,cis-muconic acid (ccMA), a fermentation-derived platform intermediate. By varying cation identity while maintaining constant anion composition, the study isolates the effects of cation size, hydration energy, and specific adsorption. Electrochemical techniques including cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) are employed, complemented by quantitative proton nuclear magnetic resonance (¹H-NMR) for product analysis. Together, these results provide mechanistic insight into how electrolyte cations influence catalytic activity, informing the design of efficient, low-carbon electrocatalytic systems for integration with biomanufacturing.