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Abstract High-performance earth-abundant electrocatalysts for oxygen and hydrogen evolutions are highly desired for renewable energy but remain challenging. Herein, we have developed ultrathin NiFeP nanosheets, and merged the NiFeP with a 3D support of sponge-like strutted graphenes (SG). The synthesized NiFeP/SG, a porous monolith, shows efficient electrocatalytic activities for oxygen and hydrogen evolutions in alkaline electrolyte with low overpotentials of 218 and 115 mV, respectively. Using NiFeP/SG as direct catalytic electrodes, the overall water splitting requires a low cell voltage of 1.54 V to achieve a current of 10 mA cm−2. The high performances result from the shifted-up d states caused by iron incorporation, the ultrathin NiFeP, and the 3D network structure of SG. Additionally, NiFeP/SG demonstrates excellent gravimetric catalytic activities, meaningful to aerospace and portables. The material opens the way to a universal robust lightweight catalytic electrode for a variety of applications in electrochemical energy storage and conversion. Graphical abstract Ultrathin NiFeP nanosheets are grown on 3D self-supported strutted-graphene foams. The lightweight porous monolith is directly applied as catalytic electrodes for bifunctionally efficient electrolysis of water. A low voltage of 1.54 V of the electrolyzer drives a current of 10 mA cm−2 for the overall water splitting in alkaline media. fx1 Highlights • A 3D strutted graphene foam is applied as the high-surface-area conductive stable lightweight support to load catalysts. • Ultrathin NiFeP nanosheets are grown on the graphene foam, serving as self-supported binder-free porous monolithic electrodes. • NiFeP/strutted-graphene shows excellent catalytic activities and remarkable gravimetric activities for both oxygen and hydrogen evolutions. • The catalytic electrode requires a low voltage of 1.54 V to deliver 10 mA cm−2 for overall water splitting in alkaline media. [ABSTRACT FROM AUTHOR]