Rational Construction of a Cu–Cu ₂ O–CuHCF Heterojunction Interface for High-Performance Potassium-Ion Sensing

The deployment of potassium ion (K⁺) sensors in demanding environments, such as marine resource utilization, energy storage systems, and industrial processes, is severely limited by the thermal instability of state-of-the-art sensing materials. Traditional ionophores like valinomycin and crown ethers irreversibly lose activity above 50 °C, rendering them unsuitable for applications involving significant temperature fluctuations. Herein, we report a breakthrough all-solid-state K⁺ sensor engineered to overcome this fundamental limitation. The sensor architecture integrates a Cu₂O semiconductor as an ion-electron transduction layer and a potassium-copper hexacyanoferrate (CuHCF(K)) active layer, forming a robust Cu-Cu₂O-CuHCF heterojunction. First-principles density functional theory (DFT) calculations guided the rational design, predicting superior K⁺ selectivity over Na⁺ based on adsorption energetics and d-band center analysis. A one-step electrochemical synthesis protocol was developed to fabricate this heterostructure with comprehensive characterization (EIS, XPS, XRD, SEM) confirming its successful formation and interfacial properties. The sensor demonstrates exceptional analytical performance, operating reliably within a wide temperature range of 25-100 °C and maintaining high selectivity for K⁺ in high-salinity seawater matrices. Furthermore, to bridge the gap between laboratory data and field deployment, we developed and open-sourced a Potential-Temperature-Concentration (PTC) machine learning model based on a back-propagation neural network. This work provides a new paradigm for designing robust electrochemical sensors for harsh environments, combining theoretical material design with intelligent data processing for practical industrial applications.