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We report on the first fabrication of vertically oriented niobium–zirconium oxynitride nanotube arrays and their use as an attractive and robust material for visible-light-driven water oxidation. These nanotube arrays with an average diameter of ∼120 nm and very short length ∼90 nm were synthesized via one-step anodization of Nb–Zr alloy sheet in NH4F-containing electrolytes. Ammonolysis of the nanotubes resulted in narrowing the bandgap energy from 3.23 to ∼2.67 eV. The Nb–Zr oxynitride nanotube arrays showed approximately an enhancement of about 1900% over that reported for thin film electrodes made of niobium oxynitride and 3700% greater than that recorded for nitrogen-doped mesoporous Nb2O5. Mott–Schottky and the valence band XPS analyses revealed the favorable band positions of the fabricated oxynitride nanotubes with respect to the water redox potentials with very high charge carriers density. The photocurrent transient measurements revealed the remarkable stability of the fabricated oxynitride nanotubes.

Designing highly active, durable, and nonprecious metal‐based bifunctional electrocatalysts for overall water electrolysis is of urgent scientific importance to realize the sustainable hydrogen production, which remains a grand challenge. Herein, an innovative approach is demonstrated to synthesize flower‐like 3D homogenous trimetallic Mn, Ni, Co phosphide catalysts directly on nickel foam via electrodeposition followed by plasma phosphidation. The electrochemical activity of the catalysts with varying Mn:Ni:Co ratios is assessed to identify the optimal composition, demonstrating that the equimolar trimetallic phosphide yields an outstanding HER catalytic performance with a current density of 10 mA cm−2 at an ultra‐low overpotential of ~14 mV, outperforming the best reported electrocatalysts. This is asserted by the DFT calculations, revealing strong interaction of the metals and the P atom, resulting in enhanced water activation and optimized GH* values for the HER process. Moreover, this optimal composition appreciably catalyzes the OER by exposing more intrinsic active species in‐situ formed on the catalyst surface during the OER. Therefore, the Mn1‐Ni1‐Co1‐P‐(O)/NF catalyst exhibits a decreased overpotential of ~289 mV at 10 mA cm−2. More importantly, the electrocatalyst sustains perfect durability up to 48 h at a current density of 10 mA cm−2 and continued 5000 cycling stability for both HER and OER. Meanwhile, the assembled MNC‐P/NF||MNC‐P/NF full water electrolyzer system attains an extremely low cell voltage of 1.48 V at 10 mA cm−2. Significantly, the robust stability of the overall system results in a remarkable current retention of ~96% after a continuous 50‐h run. Therefore, this study provides a facile design and a scalable construction of superb bifunctional ternary MNC‐phosphide electrocatalysts for efficient electrochemical energy production systems.

Designing efficient and stable water splitting photocatalysts is an intriguing challenge for energy conversion systems. We report on the optimal fabrication of perfectly aligned nanotubes on trimetallic Ti–Mo–Fe alloy with different compositions prepared via the combination of metallurgical control and facile electrochemical anodization in organic media. The X-ray diffraction (XRD) patterns revealed the presence of composite oxides of anatase TiO2 and magnetite Fe3O4 with better stability and crystallinity. With the optimal alloy composition Ti–(5.0 atom %) Mo–(5.0 atom %) Fe anodized for 16 h, enhanced conductivity, improved photocatalytic performance, and remarkable stability were achieved in comparison with Ti–(3.0 atom %) Mo–(1.0 atom %) Fe samples. Such optimized nanotube films attained an enhanced photocatalytic activity of ∼0.272 mA/cm2 at 0.9 VSCE, which is approximately 4 times compared to the bare TiO2 nanotubes fabricated under the same conditions (∼0.041 mA/cm2 at 0.9 VSCE). That was mainly correlated with the emergence of Mo and Fe impurities within the lattice, providing excess charge carriers. Meanwhile, the nanotubes showed outstanding stability with a longer electron lifetime. Moreover, carrier density variations, lower charge transfer resistance, and charge carriers dynamics features were demonstrated via the Mott–Schottky and electrochemical impedance analyses.

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