Synergistic multielectron catalysis in insoluble ammonium phosphomolybdate for electrochemical dopamine sensing

Abstract

This work presents a facile synthesis of insoluble rhombododecahedral ammonium phosphomolybdate (NH₄)₃PMo₁₂O₄₀ (APM) with a Keggin-type structure via a one-step hydrothermal method, addressing the dissolution issue of polyoxometalates (POMs) in electrolytes. The APM-modified glassy carbon electrode (APM@GCE) can catalyze the oxidation of dopamine (DA) based on the “adsorption enrichment-multielectron catalysis” mechanism. The oxidation of DA on APM@GCE is an adsorption-controlled process, primarily relying on the electrostatic interaction between protonated DA and [PMo₁₂O₄₀]³⁻, as well as the π–π stacking interaction between the benzene ring of DA and the MoO bonds of APM. The multi-electron properties of the Keggin structure in APM exert a significant catalytic effect on the oxidation of DA, enabling DA to lose 2H⁺/2e⁻ to being oxidized to dopaminoquinone. Via differential pulse voltammetry (DPV), it shows a sensitivity of 1.48 µA µM⁻¹ cm⁻², a limit of detection (LOD) of 0.031 µM, and resistance to ascorbic acid interference, offering insights for developing low-cost, high-performance POM-based electrochemical sensors.