Encapsulating Nickel‐Iron Alloy Nanoparticles in a Polysilazane‐Derived Micro‐/Mesoporous Si‐C‐O‐N‐Based Support to Stimulate Superior OER Activity

Abstract The in situ confinement of nickel (Ni)‐iron (Fe) nanoparticles (NPs) in a polymer‐derived microporous silicon carboxynitride (Si−C−O−N)‐based support is investigated to stimulate superior oxygen evolution reaction (OER) activity in an alkaline media. Firstly, we consider a commercial polysilazane (PSZ) and Ni and Fe chlorides to be mixed in N,N‐dimethylformamide (DMF) and deliver after overnight solvent reflux a series of Ni−Fe : organosilicon coordination polymers. The latter are then heat‐treated at 500 °C in flowing argon to form the title compounds. By considering a Ni : Fe ratio of 1.5, face centred cubic (fcc) Ni x Fe y alloy NPs with a size of 15–30 nm are in situ generated in a porous Si−C−O−N‐based matrix displaying a specific surface area (SSA) as high as 237 m 2 ⋅ g −1 . Hence, encapsulated NPs are rendered accessible to promote electrocatalytic water oxidation. An OER overpotential as low as 315 mV at 10 mA ⋅ cm −2 is measured. This high catalytic performance (considering that the metal mass loading is as low as 0.24 mg cm −2 ) is rather stable as observed after an activation step; thus, validating our synthesis approach. This is clearly attributed to both the strong NP‐matrix interaction and the confinement effect of the matrix as highlighted through post mortem microscopy observations.