Fig. 2: Manipulating the surface states of the Co2Mo3O8 electrode.
a Current density–time (j–t) curves of the pristine Co2Mo3O8 precatalyst under Protocol 3 treatment. Operating conditions: 1.51 V vs. RHE for 10 min, followed by −0.39 V for 15 h (A: pristine Co2Mo3O8, B: operation at 1.51 V for 10 min, C: operation at 1.51 V for 10 min and −0.39 V for 1 h, D: operation at 1.51 V for 10 min and −0.39 V for 15 h). Time-dependent in-situ Raman spectra of the Co2Mo3O8 precatalyst with continuously applied potentials of b 1.51 V and then c −0.39 V. d Ex-situ XRD patterns, and e SEM images of the same piece of Co2Mo3O8 precatalyst under different treatments in Protocol 3. f, g HRTEM image and EDX line-scan profiles of Co, Mo, and O elements of the Co(OH)2@Co2Mo3O8 catalyst developed through Protocol 3. (Inset shows the scanned region marked with an arrow.) h Side views of the Co2Mo3O8 (001) slab showing various adsorbates, such as H-, O- or OH-containing species, at different atomic sites on the surface, e.g. OH–Co represents the coverage of OH species on Co sites. i Two-dimensional (2D) surface Pourbaix diagrams for the Co2Mo3O8 (001) surface at 25 °C, illustrating the dependence of free energies on the potential and pH value of electrolytes, where ML represents monolayer. j The programmed protocols to develop various Co(OH)2@Co2Mo3O8 structures and to elucidate the potential-dependent structure evolution mechanism of the Co2Mo3O8 precatalyst. Details can be seen in Supplementary Fig. 15.
