For practical implementation of water splitting, development of efficient bifunctional catalytic electrodes by replacing precious metal-based electrocatalysts with transition metal-based electrocatalysts with high efficiencies and stabilities for both the hydrogen evolution reaction (HER) and oxygen evolution reaction(OER) is highly desirable. Accordingly, herein, flower-like Ni/a-Ni(OH)2 particles and nanosheet-shaped Ni/a&b-Ni(OH)2 arrays with adjustable shapes are first fabricated on a carbonized wood (CW) electrode without binders and additives via a simple electrodeposition approach. The hierarchically porous CW electrode with high active surface area provides effective triple pathways for the transport of electrons and ions and release of gas bubbles. Thus, the as-prepared Ni/Ni(OH)2/CW electrodes demonstrate low overpotentials of HER (62 mV; Ni/a&b-Ni(OH)2/CW), which is comparable to that of Pt/C catalyst, and OER (367 mV; Ni/a-Ni(OH)2/CW) in alkaline electrolytes, and the bifunctional electrocatalyst exhibits efficient performance with a cell voltage of 1.74 V at 10 mA cm−2. Furthermore, the cost-effective, eco-friendly, and easily manufactured Ni/Ni(OH)2/CW electrodes can be successfully applied to commercial batteries and solar panels, revealing the feasibilities and practicalities of bifunctional Ni/Ni(OH)2/CW electrodes as active and scalable electrodes for green energy systems of water splitting.