Production of formate via CO2/bicarbonate hydrogenation using cheap metal-based heterogeneous catalysts is attractive. Herein, we report the organometallic synthesis of a foam-like Ni@Ni(OH)2 composite nanomaterial which exhibited remarkable air stability and over 2 times higher catalytic activity than commercial Raney Ni catalyst in formate synthesis. Formate generation was reached with an optimal rate of 6.0 mmol/gcat/h at 100°C, a significantly lower operation temperature compared to the 200-260°C reported in the literature. Deep characterization evidenced that this nanomaterial was made of an amorphous Ni(OH)2 phase covering metallic Ni sites; a core-shell structure which is crucial for the stability of the catalyst. The adsorption of bicarbonates onto the Ni@Ni(OH)2 catalyst was found a kinetically relevant step in the reaction, and the Ni-Ni(OH)2 interface was found beneficial for both CO2 and H2 activation thanks to a cooperative effect. Our findings emphasize the underestimated potential of Ni-based catalysts in CO2 hydrogenation to formate, pointing out a viable strategy to develop stable, cheap metal catalysts for greener catalytic applications.