Lattice Proton Intercalation to Regulate WO3‐Based Solid‐Contact Wearable pH Sensor for Sweat Analysis

Abstract Sweat pH monitoring is a routine indicator in wearable biotechnology. The state‐of‐the‐art wearable pH sensors mostly rely on organic materials but face the risk of biological toxicity. WO 3 is a typical H + ‐sensitive inorganic material with chemical stability, biocompatibility, and low cost but low sensitivity and slow response. Lattice H + intercalation is herein proposed as an efficient approach that can greatly improve the sensitivity and selectivity of WO 3 ‐based pH sensors. Specifically, lattice H + intercalation can promote WO 3 from the monoclinic phase to cubic phase, which enhances the ion exchange capacity between WO 3 and H + . The resistance decreases more than two orders of magnitudes, which improves the interfacial charge transport. The occupancy of lattice H + leads to ion exchange only with H + , thus increasing the H + recognition. The intercalated H x WO 3 exhibits much improved sensitivity, reversibility, and response time. Additionally, the H x WO 3 is integrated with a solid reference electrode on a miniaturized chip for wearable sweat pH monitoring. The pH sensor exhibits good potential response even at curving over 270°. On‐body sweat pH measurments show high accuracy compared with ex situ analyses. This work emphasizes the concept of lattice proton intercalation to regulate the H + recognition of solid contacts.