Electrocatalytic water splitting at nitrogen-doped carbon layers-encapsulated nickel cobalt selenide

Generally, the catalytic overpotentials of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are unavoidable because of the low charge transfer. In this work, two strategies of alloying of Co with Ni and enclosing of electrocatalysts with carbonaceous materials were both used to accelerate the catalytic efficiency of cobalt selenide for water splitting. The nitrogen-doped carbon (NC) layer improves the reaction kinetics by efficient charge transfer. The alloying of metal into composited electrocatalysts can modify the electronic properties of host materials, thereby tuning the adsorption behavior of intermediate and improving the electrocatalytic activity. As expected, Nyquist plots reveal that the charge-transfer resistance (Rct) of nickel cobalt selenide encapsulated into nitrogen-doped carbon layer (CoNiSe/NC-3, Co:Ni = 1:1) are just 5 and 9 Ω for HER and OER, respectively, which are much lower than those of CoSe/NC-1 (Co:Ni = 1:0) (81 and 138 Ω) and CoNiSe/NC-3 without NC (CoNiSe-3) (54 and 25 Ω). With the high charge transfer and porous structure, CoNiSe/NC-3 shows good performance for both HER and OER. When current density reaches 10 mA cm−2, only 100 and 270 mV overpotentials are required for HER and OER, respectively. With the potential of 1.65 V, full water splitting also can be catalyzed by CoNiSe/NC-3 with current density of 20 mA cm−2, suggesting that CoNiSe/NC-3 could be used as replacement for noble metal electrocatalysts.