Covalent bond modulation of charge transfer for sensitive heavy metal ion analysis in a self-powered electrochemical sensing platform

Abstract

Rational design of photoelectric active materials for photoanodes in photocatalytic fuel cells is crucial for developing highly sensitive self-powered electrochemical sensors. Achieving directional migration and shortening transmission pathways of charge in photoanodes remains a fundamental challenge for enhancing the oxygen evolution reaction performance of photocatalytic fuel cells. Herein, tungsten species atomically dispersed on carbon-rich graphitic carbon nitride (W-CN-C) with the N–W–O covalent bond was designed as the photoanode for constructing a self-powered photocatalytic fuel cell sensing of heavy metal copper ions. W-CN-C was synthesized by self-assembly, exfoliation, and thermal-induced treatment processes. The N–W–O covalent bonds by anchoring tungsten atoms on carbon-rich carbon nitride served as an interfacial charge transport channel, facilitating the separation and migration of charge carriers. The carbon content increase by forming a carbon-rich structure can enhance π-electron delocalization in the W-CN-C, significantly broadening sunlight utilization range. The dispersed tungsten atoms provide effectively active sites, promoting the kinetics of the oxygen evolution reaction between the W-CN-C photoanode and electrolyte interface. The synergistic effects significantly enhance the visible light absorption ability and charge separation and transfer efficiency, improving the photoelectric conversion efficiency of W-CN-C photoanode, exhibiting superior oxygen evolution reaction performance, leading to the amplified open circuit potential in the photocatalytic fuel cell system based on excellent oxygen reduction reaction performance of the Pt@C electrocatalyst cathode. The specific identification probe for copper ions was effectively anchored on the W-CN-C photoanode to construct a self-powered photocatalytic fuel cell sensing platform for copper ions detection. The complex formed by copper ions with the probe hindered electron transport at the W-CN-C photoanode, altering the output detection signal of the photocatalytic fuel cell, thus demonstrating a broad detection range spanning five orders of magnitude (2.0× 10⁻² ∼ 9.2 × 10² nmolmol∙L⁻¹), a low limit of detection (7.0 pmol∙L⁻¹), high selectivity against common interferents, and applicability for detecting heavy metal copper ions in the aquatic environment. Furthermore, the platform allowed for self-powered and portable determination of copper ions using a multimeter as a signal output device, achieving a detection range of 0.25 ∼ 1.3 × 10² nmol∙L⁻¹ and a limit of 84 pmol∙L⁻¹. This work proposes an approach for developing a high-performance photoanode utilizing atomically dispersed metals to introduce covalent bonds as charge transfer channels, paving the way for highly sensitive self-powered electrochemical sensors for environmental monitoring.