Edge overgrowth of spiral bimetallic hydroxides ultrathin-nanosheets for water oxidation† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5sc00836k Click here for additional data file.

Experiment Section Synthesis of spiral ultrathin-nanosheets with overgrew edge (SUNOE): For NiFe SUNOE, 0.114g NiCl24H2O and 0.060g (NH4)2Fe(SO4)26H2O were weighed and transferred into a 40mLpolytetrafluoroethene autoclave. Then 8 mL ethanol were added to dissolve the salts by sonication. Though the sulfate seemed not fully dissolved, 2mL oleylamine (OAm) was injected into the autoclave, some precipitate appeared immediately. The solution became transparent again as 30mL hexane was adding into the system. For NiCo SUNOE, 0.024g NiCl24H2O and 0.014g CoSO47H2O were added into an 11mLpolytetrafluoroethene autoclave. Then 2mL ethanol was injected to dissolve salts. While the CoSO47H2O was not fully dissolved, the solution showed a blue color. The color went darker when 0.5mL OAm was added. Then 8mL hexane was transferred into the autoclave. For CoFe SUNOE, 0.014g CoCl24H2O and 0.009g (NH4)2Fe(SO4)26H2O were added into an 11mLpolytetrafluoroethene autoclave. Then 0.5mL octylamine and 8mL hexane were added in sequence. The sulfates could not fully dissolve in ethanol, but they didn’t affect the formation of SUNOE with both cations, since the amine would help to further dissolve the salts. After all these steps were done, seal the autoclave and put it into oven set temperature at 140oC and 8 hours to react. After cooling down, the products were washed 3 times by using ethanol and centrifugating at 10000 rpm for 5 minutes. Then samples were dispersed in 10mL cyclohexane for NiFe SUNOE and 2mL cyclohexane for NiCo and CoFe SUNOE. Dilute the solution and drop a drop on TEM grid for morphology test. All the chemicals except OAm were purchased from Sinopharm Chemical Reagent Co., Ltd, OAm was obtained from Acros. The ratio of salts, amine and solvent are optimized to get pure SUNOE. Slightly changing them could also result in similar SUNOE, but less purities. Substituting the chloride salts with nitrate salts would also synthesize SUNOE, but less purities, while changing the amount of sulfate would dramatically change the morphology, this means it’s not the chloride but sulfate are vital to form SUNOE.