Green Route to the Synthesis of Synergic 4f(Re)–3d(TM) Heterobimetallic CeCoCH Nanorice for Robust Industrially Relevant Water Splitting

To regulate transition metal (TM)-based electrocatalysis, rare earth (RE) elements have emerged as key promoters; however, investigation into the RE-enhanced activity of TMs in water splitting reactions is limited. Herein, we used the expired metformin (MF) drug as an organic host to synthesize an RE-TM carbonate hydroxide (MF-CeCoCH) to explore the origin of the Ce-triggered kinetics of Co sites in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The Ce-coupling with MF-CoCH increased the active surface area to expose more active sites and regulated the electronic redistribution of Co sites to boost the specific activity. MF-CeCoCH exhibits exceptional activity with a high durability. The reaction kinetics of the catalysis was monitored via in situ electrochemical impedance spectroscopy (EIS) and the demand for less activation energy after Ce-coupling was revealed by Arrhenius. The doped bimetal cations showed a smaller energy of activation (<i>E</i>_a), analogous to higher activity, yet site reconstruction is less likely to occur. The higher rate constant derived from the Trumpet plot for MF-CeCoCH at various pH values indicates the vigorous formation of gas bubbles. Alkaline and solar-driven electrolyzers of MF-CeCoCH^(*,-) have been explored for total water splitting at 1.58 V, giving an output of 10 mA cm^-2. The exceptional Ce-4f valence electronic structure endows Co sites with differentiated regulation of HER and OER via Ce-4f-Co-3d orbital coupling. In HER, the retained Ce-4f state triggered *H intermediate adsorption, while in OER, the Ce-4f band was sacrificed and provided additional spin coupling with O-intermediates.