Surface-Oxidized Dicobalt Phosphide Nanoneedles as a Nonprecious, Durable, and Efficient OER Catalyst

Needle-shaped narrow hexagonal phase 1D nanostructures of dicobalt phosphide (Co₂P) are reported as efficient electrocatalysts for the oxygen evolution reaction (OER). Without other metal incorporation, which was typically followed for enhancing the OER activity, the electrochemical performance was observed to be superior in comparison to all reported cobalt-based nanostructured metal phosphides. For anodic metamorphosis, these nanostructures, like all other metal phosphides, undergo surface oxidation but remain more active and superior to pure cobalt oxides as well as surface-oxidized different shaped monocobalt phosphides. Moreover, the synthesis was also followed by adopting a moderate synthetic protocol where PH₃ gas was used as a phosphorus source and also scaled up to the gram level. In addition, the hydrogen evolution reaction (HER) performance of these phosphides was further studied, and the performance was observed to be comparable to that in the best reports

Synergistic Effect of Inactive Iron Oxide Core on Active Nickel Phosphide Shell for Significant Enhancement in Oxygen Evolution Reaction Activity

A unique core–shell nanostructured oxygen evolution reaction (OER) catalyst composed of an electrochemically inactive crystalline iron oxide core and an active amorphous nickel phosphide shell is presented, and this catalyst results in superior OER activity. Even activators enhancing the activity of the OER catalyst by promoting the redox reactions are reported, but here the exclusive position of iron in the nanostructures indeed boosted the efficiency due to ideal placement. Moreover, these nanostructures are also prepared in a sophisticated mechanistic approach in which selectively one metal is phosphidated and the other is not. Interestingly, in the absence of iron, nickel phosphide crystallized in a different shape, but in the presence of iron, this specifically formed amorphous Ni_<i>x</i>P became more efficient for promoting the OER. Details of the formation of this active catalyst are studied; the electrochemical reactions are investigated, and the OER activity is compared with that of different leading metal phosphides

Urea-Assisted Room Temperature Stabilized Metastable β‑NiMoO₄: Experimental and Theoretical Insights into its Unique Bifunctional Activity toward Oxygen Evolution and Supercapacitor

Room-temperature stabilization of metastable β-NiMoO₄ is achieved through urea-assisted hydrothermal synthesis technique. Structural and morphological studies provided significant insights for the metastable phase. Furthermore, detailed electrochemical investigations showcased its activity toward energy storage and conversion, yielding intriguing results. Comparison with the stable polymorph, α-NiMoO₄, has also been borne out to support the enhanced electrochemical activities of the as-obtained β-NiMoO₄. A specific capacitance of ∼4188 F g^–1 (at a current density of 5 A g^–1) has been observed showing its exceptional faradic capacitance. We qualitatively and extensively demonstrate through the analysis of density of states (DOS) obtained from first-principles calculations that, enhanced DOS near top of the valence band and empty 4d orbital of Mo near Fermi level make β-NiMoO₄ better energy storage and conversion material compared to α-NiMoO₄. Likewise, from the oxygen evolution reaction experiment, it is found that the state of art current density of 10 mA cm^–2 is achieved at overpotential of 300 mV, which is much lower than that of IrO₂/C. First-principles calculations also confirm a lower overpotential of 350 mV for β-NiMoO<sub>4.</sub

Simple Growth of Faceted Au–ZnO Hetero-nanostructures on Silicon Substrates (Nanowires and Triangular Nanoflakes): A Shape and Defect Driven Enhanced Photocatalytic Performance under Visible Light

A simple single-step chemical vapor deposition (CVD) method has been used to grow the faceted Au–ZnO hetero-nanostructures (HNs) either with nanowires (NWs) or with triangular nanoflakes (TNFs) on crystalline silicon wafers with varying oxygen defect density in ZnO nanostructures. This work reports on the use of these nanostructures <i>on</i> substrates for photodegradation of rhodamine B (RhB) dyes and phenol under the visible light illumination. The photoluminescence measurements showed a substantial enhancement in the ratio of defect emission to band-edge emission for TNF (ratio ≈ 7) compared to NW structures (ratio ≤ 0.4), attributed to the presence of more oxygen defects in TNF sample. The TNF structures showed 1 order of magnitude enhancement in photocurrent density and an order of magnitude less charge-transfer resistance (<i>R</i>_ct) compared to NWs resulting high-performance photocatalytic activity. The TNFs show enhanced photocatalytic performance compared to NWs. The observed rate constant for RhB degradation with TNF samples is 0.0305 min^–1, which is ≈5.3 times higher compared to NWs case with 0.0058 min^–1. A comparison has been made with bulk ZnO powders and ZnO nanostructures without Au to deduce the effect of plasmonic nanoparticles (Au) and the shape of ZnO in photocatalytic performance. The results reveal the enhanced photocatalytic capability for the triangular nanoflakes of ZnO toward RhB degradation with good reusability that can be attracted for practical applications