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Nickel, cobalt, and manganese oxides are easily obtainable non-noble metal catalysts for water splitting. However, the relationship between composition and catalysts' performance still needs systematic studies. Herein, guided by theoretical calculations, a low overpotential, easily prepared Mn-doped Co3O4 was deposited on graphite plates for water splitting. The 30% Mn-doped Co3O4 (Co2.1Mn0.9O4) required the lowest overpotential for oxygen evolution reaction (OER), in which the Co2.1Mn0.9O4 reached 20, 30, and 50 mA cm−2 in the overpotentials of 425, 451, and 487 mV, respectively, with 90% IR compensation. Under overall water-splitting conditions, the current density reached 30 mA cm−2 at an overpotential of 0.78 V without IR compensation. Charge density difference analysis illustrates that doped Mn provides electrons for O atoms, and that Mn doping also promotes the electron fluctuation of Co atoms. XPS analysis reveals that Mn-doping increases the chemical valence of the Co atom, and that the doped Mn atom also exhibits higher chemical valence than the Mn of Mn3O4, which is advantageous to boost the form of based-OOH* radical, then decrease the overpotential. Considering the particular simplicity of growing the Co2.1Mn0.9O4 on graphite plates, this work is expected to provide a feasible way to develop the high-performance Co-Mn bimetallic oxide for water splitting. [ABSTRACT FROM AUTHOR]

• A novel binary metal sulfide Ni 3 Bi 2 S 2 is predicted to be synthesized from Bi 2 S 3 and Ni powder using DFT calculation. • Ni 3 Bi 2 S 2 proved a high-capacity, high-reversible, and easy-synthesized anode for sodium-ion batteries first. • Heterojunction-like Ni 3 Bi 2 S 2 /NiS-G composites surpassing most of the recently-reported same-type of sodium-ion batteries. In the context of scalable electrode production via ball-milling, achieving high cycling stability and electrochemical performance in bifunctional anodes for sodium ion batteries (SIBs) is crucial yet remains a significant challenge. To address these objectives, we have developed a unique hybrid anode nanocomposite characterized by its local multiphase nature. This composite involves the incorporation of novel ternary-Ni-Bi-S/binary-Ni-S nanomaterials onto exfoliated graphite nanosheets (Ni 3 Bi 2 S 2 /NiS-G) through a facile ball-milling process. Our combined experimental and theoretical investigations suggest that the interactions between graphite nanosheets and the layered structure of Ni 3 Bi 2 S 2 /NiS, along with the discharge products of Na 2 S, play pivotal roles in enhancing the Na+ diffusion rate and stability of the hierarchical configuration anode. Upon testing, the novel Ni 3 Bi 2 S 2 /NiS-G shows overwhelmingly higher electrochemical performance compared to the Ni 3 Bi 2 S 2 /NiS counterpart, the Ni 3 Bi 2 S 2 /NiS-G delivered a reversible capacity of 489.9 mAh/g at 0.2 A/g after 400 cycles, and displayed a high capacity of 387.3 and 339.6 mAh/g after 500 cycles at 1 A/g and 2 A/g, respectively, yielding a high capacity retention ratio of 84.8 % and 82.8 % of the 1st cycle. This work provided a novel approach for developing new bifunctional anode electrodes with high capacity and rate performance as well as superior cycling stability. [ABSTRACT FROM AUTHOR]