Bimetallic Layered Hydroxide Nitrate@Graphene Oxide as an Electrocatalyst for Efficient Non-Enzymatic Glucose Sensors: Tuning Sensitivity by Hydroxide-Regulated M2(OH)4–n(An–) Phases Derived from Solvent Engineering

Owing to their high catalytic activity, transition metal hydroxides are promising electrocatalysts for non-enzymatic glucose sensors. The hydroxyl functionalities in Co 1– x Ni x hydroxide/mixed anionic hydroxides play a vital role in their electrochemical activation via conversion to an oxyhydroxide catalyst and thus impact their sensitivity to small molecule (glucose) oxidation. Herein, we report the rational synthesis of M 2 (OH) 4– n (A n – ) compositions (0 > n ≤ 2) with hydroxide (OH)-rich and OH-deficient phases, viz., CoNi-hydroxide nitrate (CoNi-HN) and CoNi-hydroxide carbonate (CoNi-HC), by using different solvents of ethanol and water, under solvo/hydrothermal conditions, respectively. The OH-rich CoNi-HN phase exhibited enhanced pre-activation efficiency, which accelerated the glucose oxidation kinetics, and beneficial morphological features (flower-like structures with interconnected nanosheets). The OH-rich CoNi-HN catalyst, which is the first report for a glucose sensor, exhibited superior sensing property with a high sensitivity of ∼136 μA mM –1 cm –2 . The structure–(sensing) property relationship was analyzed in detail by tailoring the morphology to form an OH-rich graphene oxide (GO) hybrid. The CoNi-HN/GO hybrid exhibited improved glucose oxidation, delivering a wide glucose-sensing range, with a sensitivity of ∼268 μA mM –1 cm –2, a low detection limit of 28.5 μM (S/N = 3), and good selectivity. The excellent sensitivity of this hybrid was attributed to the synergism between the OH-rich CoNi-HN phase and the OH-rich interfaces between GO and CoNi-HN, as well as a unique flower-like morphology with interconnected nanosheets. Insights into the critical role of hydroxyl groups in the electrocatalytic performance of transition-metal-based catalysts have been emphasized in this work.