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Hierarchical flower-like NiCo 2 O 4 anchored on multiwalled carbon nanotubes (NiCo 2 O 4 -MCNTs) act as robust bifunctional electrocatalysts towards O 2 (OER) and H 2 (HER) evolution reactions. The NiCo 2 O 4 -MCNTs hybrid is synthesized in a facile surfactant-free hydrothermal process, and its flower-like morphology was shown to consist of 1D nanowires. The MCNT support is beneficial for enhanced reactive sites, efficient charge transfer, and durability of the composite. The material shows low overpotentials of 350 mV and 209 mV for OER and HER, respectively at 10 mA cm À 2 . Such values are comparable to contemporary noble-metal catalysts and even lower than reported non-precious catalysts. Moreover, this hybrid shows high current density, lower Tafel slope, and excellent stability. The synergistic coupling effects between the MCNTs and NiCo 2 O 4 are key factors for the superior catalytic activity of these hybrid materials.[a] Dr. blocking electrodes were laid on both sides of the pellet by pressing at 200 MPa. The electrical conductivity (σ) of the samples at room temperature were obtained from the dc polarizations (current, I vs. time, t curves) in Figure S4, using the following Equations (1) and (2): 4 5 6 7 8

The 3d transition metals were incorporated into SBA-15 matrix by co-condensation synthesis method. Very low concentrations of metals were introduced into silica framework by maintaining the metal to silica ratio in the synthesis gel at 0.01. The difference in hydrolysis rates of metal and silica precursors have led to textural modifications while demonstrating the structural integrity akin to pristine SBA-15. The physicochemical properties obtained offer some insights into the P123 micelle aggregation and mechanism of formation of silica network in the presence of metal salts under similar synthesis conditions of pure SBA-15. The metal doping into SBA-15 leads to increased pore diameters. Higher lattice constants (a 0 ) observed in these samples are attributed to the increased pore wall thickness. The significant retention of the hexagonal mesostructure seen in LXRD indicates diminutive influence of metal salts at lower concentrations. Macroscopic morphologies studied by SEM show the formation of spheres along with conventional fibre-like rods.

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