NiFeOOH-Co<sub>9</sub>S<sub>8</sub>-Intercalated Nanostructure Arrays for Energy-Efficient H<sub>2</sub> Production and Sulfion Oxidation at High Current Density
Santosh Semwal, Renna Shakir, J. Karthikeyan, Akhoury Sudhir Kumar Sinha, Umaprasana Ojha
Abstract
Though electrocatalysts displaying efficacy for the hydrogen evolution reaction (HER) or sulfion oxidation reaction (SOR) individually are available in the literature, systems exhibiting proficiency toward the HER and SOR together are desirable to produce H 2 in a robustly energy-efficient manner. Furthermore, simultaneous facile growth and intercalation of multiple nanocatalyst systems to achieve the above objective are synthetically challenging. Herewith, the reactivity preferences of Lewis acid (FeCl 3 ) and salt [Co(NO 3 ) 2 ] are utilized to longitudinally grow NiFeOOH-Co 9 S 8 - n intercalated nanostructure arrays of varied Fe:Co ratios on Nickel foam using a one-step procedure at low temperature (50 °C). The NiFeOOH-Co 9 S 8 - n exhibit bifunctionality and H 2 production at a relatively high j value of 1000 mA/cm 2 is realized at a low overall potential (SOR + HER) value of 0.84 V in NaOH (1.0 M)-Na 2 S (1.0 M). The efficiency of the electrode enabled the SOR j value to reach 1000 mA/cm 2 at 0.72 V in 1.0 M Na 2 S solution in the absence of NaOH. The density functional theory analysis revealed that the oxide doping of the Co 9 S 8 facilitated by the FeOOH-Co 9 S 8 intercalation promoted the electrocatalytic activity. The nanocatalyst promotes highly energy-efficient and sustainable H 2 production, where a j value of 100 mA/cm 2 under the electrolyzer mode is realized at an unprecedented potential of 0.44 V (iR-uncorrected) and ultralow power consumption (11.8 kW h/kg H 2 ), which is minimum among reported systems suggesting its viability toward commercial production of H 2 in future.