Engineering Surface Atomic Structure Of Single-crystal Cobalt(?)oxide Nanorods For Superior Electrocatalysis

Earth abundant transition metal oxide?TMO?-based catalysts are promising electro-catalysts which may achieve ultrahigh catalytic activity and durability for OER/ORR;However,it is acknowledged that the electronic conductivity of TMOs is relatively poor,greatly limiting their electrocatalytic activities,and pure TMOs are generally considered as HER inactive materials due to their inappropriate hydrogen adsorption energy.Hence,the synthesis of TMO catalysts with high activity and good durability,and the study of atomic,electronic structure and catalytic properties of these nanostructures are of broad scientific significance and great technological importance.However,the application of efficient TMO catalysts in electrocatalysis is in its infancy.Also,engineering surface atomic structure and understanding their role in electrocatalysis at the atomic level is still lacking.Firstly,a bi-functional,binder-free,non-noble-metal based SC CoO NRs were successfully fabricated onto the CFP through gas phase cation exchange using ZnO NWs as templates.HADDF-STEM results evidently demonstrate that the surface of SC CoO NRs is enclosed with 3D nano-sawtooth and preferentially expose{111}facets,which is estimated to be 46%of the total surface area.A combination of XANES and XPS results confirmed the presence of abundant O-vacancies on the surface of SC CoO NRs.The HAADF-STEM and XRD results indicating that tensile strain are dominantly enriched on the surface of S-CoO NRs?near below 2⁵ nm?.Secondly,as-synthesized SC CoO NRs exhibit outstanding ORR/OER activity.The SC CoO NRs show a lower onset potential of 0.96 V?vs.RHE?,E_1/2=0.85 V?vs.RHE?and a Tafel slope of 47 mV/dec,which close to Pt catalysts.Moreover,the SC CoO NRs achieve an enhanced current density of 10 mA/cm² at 1.56 V?vs.RHE?,which is better than RuO₂.Furthermore,the SC CoO NRs exhibit an outstanding overall electrode activity?E=0.71 V,which outperforming the most of the reported highly active reversible oxygen catalysts.Our experimental and theoretical results suggest that proper combination of O-vacancies and{111}facets yield the enhanced charge transfer and optimal reaction pathways for both ORR/OER,which enable SC CoO NRs to achieve the highest overall oxygen electrode activity.Finally,on the basis of experimental observations and theoretical calculations,we demonstrated that the tensile strain located on the outermost surface of CoO NRs results in the creation of a large quantity of O-vacancies that facilitate water dissociation,and modulate the electronic structure to weaken hydrogen adsorption toward the optimum region.We emphasize that the activity of the strained CoO NRs is located in proximity of the top of the volcano-shaped plot for HER catalysts,and the introduction of tensile strain on the surface of CoO NRs can turn an inactive material into a highly efficient electrocatalyst toward HER.