title: CoSe₂ and NiSe₂ Nanocrystals as Superior Bifunctional Catalysts for Electrochemical and Photoelectrochemical Water Splitting.
abstract: Catalysts for oxygen evolution reactions (OER) and hydrogen evolution reactions (HER) are central to key renewable energy technologies, including fuel cells and water splitting. Despite tremendous effort, the development of low-cost electrode catalysts with high activity remains a great challenge. In this study, we report the synthesis of CoSe2 and NiSe2 nanocrystals (NCs) as excellent bifunctional catalysts for simultaneous generation of H2 and O2 in water-splitting reactions. NiSe2 NCs exhibit superior electrocatalytic efficiency in OER, with a Tafel slope (b) of 38 mV dec(-1) (in 1 M KOH), and HER, with b = 44 mV dec(-1) (in 0.5 M H2SO4). In comparison, CoSe2 NCs are less efficient for OER (b = 50 mV dec(-1)), but more efficient for HER (b = 40 mV dec(-1)). It was found that CoSe2 NCs contained more metallic metal ions than NiSe2, which could be responsible for their improved performance in HER. Robust evidence for surface oxidation suggests that the surface oxide layers are the actual active sites for OER, and that CoSe2 (or NiSe2) under the surface act as good conductive layers. The higher catalytic activity of NiSe2 is attributed to their oxide layers being more active than those of CoSe2. Furthermore, we fabricated a Si-based photoanode by depositing NiSe2 NCs onto an n-type Si nanowire array, which showed efficient photoelectrochemical water oxidation with a low onset potential (0.7 V versus reversible hydrogen electrode) and high durability. The remarkable catalytic activity, low cost, and scalability of NiSe2 make it a promising candidate for practical water-splitting solar cells.
authors: Department of Chemistry, Korea University , Jochiwon 339-700, Korea.
authors: In Hye
authors: IH
authors: Kwak
authors: Department of Chemistry, Korea University , Jochiwon 339-700, Korea.
authors: Hyung Soon
authors: HS
authors: Im
authors: Department of Chemistry, Korea University , Jochiwon 339-700, Korea.
authors: Dong Myung
authors: DM
authors: Jang
authors: Graduate School of Green Energy Engineering, Hoseo University , Asan 336-795, Korea.
authors: Young Woon
authors: YW
authors: Kim
authors: Department of Chemistry, Korea University , Jochiwon 339-700, Korea.
authors: Kidong
authors: K
authors: Park
authors: Department of Chemistry, Korea University , Jochiwon 339-700, Korea.
authors: Young Rok
authors: YR
authors: Lim
authors: Graduate School of Green Energy Engineering, Hoseo University , Asan 336-795, Korea.
authors: Eun Hee
authors: EH
authors: Cha
authors: Department of Chemistry, Korea University , Jochiwon 339-700, Korea.
authors: Jeunghee
authors: J
authors: Park
keywords: CoSe2; NiSe2; Si nanowire; bifunctional; photoelectrochemical cell; water splitting