The combination of hydrogen evolution, nitric oxide oxidation and Zn-nitrate battery for energy conversion and storage by an efficient nitrogen-dopped CoOX electrocatalyst with Turing structure.

Abstract

We tuned the morphology from the needle-like Co(CO₃)_0.5(OH)·0.11H₂O to the unique Turing-structured CoCO₃ through controlling the amount of glycerol in the solvothermal system, and then synthesized the Turing structure consisting of N-50 %-CoO_X hollow nanoparticles though the Kirkendall effect during nitriding process, which was applied as a novel bifunctional self-supporting electrode for efficient electrocatalytic hydrogen evolution reaction (HER) and electrocatalytic NO oxidation reaction (eNOOR). The eNOOR can be not only used as a substitution anode reaction of oxygen evolution reaction (OER) to couple with HER for efficient water splitting, but the production of nitrate from eNOOR also provides a strategy for the development of Zn-nitrate battery. The N-50 %-CoO_X electrode showed significant HER activity and excellent stability in 1 M KOH electrolyte, with an overpotential of 30 mV at a current density of 10 mA cm^-2. While the eNOOR performance of the N-50 %-CoO_X electrode showed significantly increased NO₃^- yield of 163.2 mg cm^-2h^-1 with NO concentration of 10 %, which was far more exceeding the most advanced nitrogen electro-oxidation. It is worth mentioning that the Zn-nitrate battery showed an open circuit voltage (OCV) of 1.36 V and a power density of 1.21 mW cm^-2. Density function theory (DFT) and orbital theory results indicate that the doping of N in CoO_X facilitates the electrons transfer, and greatly reduces free energy of the decision step in the eNOOR reaction path (the second step NO*→NOOH*), leading to excellent catalytic activity. This study provides a strategy of "Killing three birds with one arrow", which can achieve the effective hydrogen production, removal of NO pollutant, and chemical energy storage of nitrate for power generation.