Atomic Layer Deposition of NiOOH/Ni(OH)2 on PIM‐1‐Based N‐Doped Carbon Nanofibers for Electrochemical Water Splitting in Alkaline Medium

: Portable and flexible energy devices demand lightweight and highly efficient catalytic materials for use in energy devices. An efficient water splitting electrocatalyst is considered an ideal future energy source. Well-aligned high-surface-area electrospun polymers of intrinsic microporosity (PIM-1)-based nitrogen-doped carbon nanofibers were prepared as a free-standing flexible electrode. A non-noble-metal catalyst NiOOH/Ni(OH)2 was precisely deposited over flexible free-standing carbon nanofibers by using atomic layer deposition (ALD). The morphology, high surface area, nitrogen doping, and Ni states synergistically showed a low onset potential (ηHER =-40 and ηOER =290 mV vs. reversible hydrogen electrode), small overpotential at η10 [oxygen evolution reaction (OER)=390.5 mV and hydrogen evolution reaction (HER)=-147 mV], excellent kinetics (Tafel slopes for OER=50 mV dec-1 and HER=41 mV dec-1 ), and high stability (>16 h) towards water splitting in an alkaline medium (0.1 m KOH). The performance was comparable with that of state-of-the-art noble-metal catalysts (e.g., Ir/C, Ru/C for OER, and Pt/C for HER). Post-catalytic characterization with X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy further proved the durability of the electrode. This study provides insight into the design of 1D-aligned N-doped PIM-1 electrospun carbon nanofibers as a flexible and free-standing NiOOH/Ni(OH)2 decorated electrode as a highly stable nanocatalyst for water splitting in an alkaline medium.