Hydrogen gas, a promising clean energy source, can be reversibly produced at high turnover rates by natural metalloenzymes known as [NiFe] hydrogenases ([NiFe]-H₂ases). Despite their potential as carbon-free catalysts, their sensitivity to oxygen limits their practical applications. To address this, nickel-substituted rubredoxin (NiRd) was developed as a robust artificial metalloenzyme model1,2. NiRd mimics both the structure and proton reduction activity of [NiFe]-H₂ases, but requires improvements in overpotential to achieve comparable efficiency. Perturbing the local electric field has proven effective in tuning redox potentials within small molecules in organic solvents3-5. To build on this approach, protein-film electrochemistry in aqueous solutions was used to study the impact of Lewis acids near the active site of NiRd, aiming to positively shift the redox potential. Three approaches were explored to position Lewis acids near the NiRd active site: (1) Exogenous outer-sphere addition; (2) Semisynthetic manipulation; and (3) Biochemical perturbations. Cyclic voltammetry revealed an unexpected negative shift in redox potential upon the addition of Lewis acids. This motivated further investigation across different conditions, including variations in pH, Lewis acid identity, concentration, and charge. The results suggest that surface charge effects play a key role in the direction and magnitude of the Lewis-acid-induced redox potential shift, leading to a broader examination of electrostatic tuning strategies in aqueous systems. This study provides valuable insight into how salts can affect the electrochemical properties of protein on an electrode surface, as well as the opportunities and limitations of using electrostatics to modulate the activity of artificial metalloenzymes and catalysts in aqueous solutions.