Fig. 4
Structural stability of m-CoSe2. a–e, SAED patterns (a), XRD patterns (b), Raman spectra (c), Co 2p XPS spectra (d), and Se 3d XPS spectra (e) of the m-CoSe2 catalyst before and after different potential cycles. Scale bar in a, 5 1/nm. f ICP-AES measurements compare the Co and Se dissolved into acidic electrolyte after different potential cycles for m-, c-, and o-CoSe2 catalysts. g Colorimetric comparison of the cycled electrolytes added in sodium acetate and nitroso-R salt solution. No color change was seen for m-CoSe2, indicating its marked structural stability in acidic electrolyte. Nitroso-R salt was used as the color indicator. The freshly-made c- and o-CoSe2 catalysts were treated in pure deionized water at 200 °C for 12 h before cycling to remove any potential unstable or amorphous components.
