Metallic Ni₃S₂ Films Grown by Atomic Layer Deposition as an Efficient and Stable Electrocatalyst for Overall Water Splitting

We describe the direct preparation of crystalline Ni₃S₂ thin films via atomic layer deposition (ALD) techniques at temperatures as low as 250 °C without postthermal treatments. A new ALD chemistry is proposed using bis(1-dimethylamino-2-methyl-2-butoxy) nickel(II) [Ni(dmamb)₂] and H₂S as precursors. Homogeneous and conformal depositions of Ni₃S₂ films were achieved on 4 in. wafers (both metal and oxide substrates, including Au and SiO₂). The resulting crystalline Ni₃S₂ layers exhibited highly efficient and stable performance as electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in alkaline solutions, with a low overpotential of 300 mV and a high turnover frequency for HER and an overpotential of 400 mV for OER (at a current density of 10 mA/cm²). Using our Ni₃S₂ films as both the cathode and the anode, two-electrode full-cell electrolyzers were constructed, which showed stable operation for 100 h at a current density of 10 mA/cm². The proposed ALD electrocatalysts on planar surfaces exhibited the best performance among Ni₃S₂ materials for overall water splitting recorded to date.