Predicting sensitivity to glucose in metal sulfides: a structural and surface characterization study

Abstract

The increasing prevalence of diabetes is leveraging the development of improved management technologies, including non-enzymatic glucose sensors that offer enhanced stability and longer operation times. However, the lack of reliable methods to predict materials' electrocatalytic activity remains a significant barrier to their advancement. Herein, we obtained transition metal sulfides ($CuS$, $Ag_{2}S$, $FeS_{2}$, and $α-NiS$) with similar shapes and sizes using wet chemical methods. Detailed structural and surface characterization revealed the presence of metals in mixed oxidation states and the formation of disulfides and polysulfides on the surface of air-exposed materials. The optical measurements supported by theoretical calculations indicated band gaps of 1.74, 0.98, and 1.14 eV in $CuS$, $FeS_{2}$, and $Ag_{2}S$, respectively. Nickel sulfide exhibited an intraband transition at 1.42 eV. The electrocatalytic activity toward glucose was investigated using cyclic voltammetry and chronamperometry. The lowest oxidation potential of 615 mV showed $α-NiS$, whereas the highest – $Ag_{2}S$ (860 mV). The sensitivity determined in chronoamperometry measurements increased in the order of $α-NiS>CuS>Ag_{2}S>FeS_{2}$. Furthermore, selectivity studies revealed that $FeS_{2}$ responded only to strong reductants, while $α-NiS$ to all examined electroactive species. In the last step, a clear relationship was identified between the d-band center position $(d_{bc})$ in metal sulfides and their electrochemical performance. The dbc relative to the Fermi level is optimal in $CuS$ and $NiS$ (around −2 eV) for forming bonds with glucose and intermediates, while in $Ag_{2}S$ and $FeS_{2}$, it lays too far or too close for effective electrooxidation.