MnMoO4 nanosheet array: an efficient electrocatalyst for hydrogen evolution reaction with enhanced activity over a wide pH range

Unraveling the MnMoO4 polymorphism: a comprehensive DFT investigation of α, β, and ω phases

The MnMoO₄ is an environmentally friendly semiconductor material widely employed in technological devices. This material can be obtained on three different polymorphs, and although such phases were reported decades ago, some obscurity over their structure and properties is still perceived. Thus, this work provides a comprehensive DFT investigation of the α, β, and ω phases of MnMoO_4, analyzing their crystalline structure, stability, and electronic and magnetic properties. The results show that all phases of MnMoO₄ are stable at room conditions connected by pressure application or long-time high-temperature treatment. The MnMoO₄ phases are G-type antiferromagnetic with semiconductor bandgap and have enormous potential to develop magnetic, optical, and electronic devices and photocatalytic-based processes. The results also evidence potential antiviral and antibacterial activities of the three MnMoO₄ polymorphs.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10853-022-07277-7.

Electronic transitions of SWCNTs in comparison to GO on Mn3O4/TiO2 nanocomposites for hydrogen energy generation and solar photocatalysis

The conductivity of metal/metal oxide-doped TiO₂ nanomaterials is enhanced by the incorporation of carbonaceous materials, e.g. single-walled carbon nanotubes (SWCNTs) and graphene oxide (GO).

Using anion photoelectron spectroscopy of cluster models to gain insights into mechanisms of catalyst-mediated H2 production from water

Metal oxide cluster models of catalyst materials offer a powerful platform for probing the molecular-scale features and interactions that govern catalysis. This perspective gives an overview of studies implementing the combination of anion photoelectron (PE) spectroscopy and density functional theory calculations toward exploring cluster models of metal oxides and metal-oxide supported Pt that catalytically drive the hydrogen evolution reaction (HER) or the water-gas shift reaction. The utility in the combination of these experimental and computational techniques lies in our ability to unambiguously determine electronic and molecular structures, which can then connect to results of reactivity studies. In particular, we focus on the activity of oxygen vacancies modeled by suboxide clusters, the critical mechanistic step of forming proximal metal hydride and hydroxide groups as a prerequisite for H2 production, and the structural features that lead to trapped dihydroxide groups. The pronounced asymmetric oxidation found in heterometallic group 6 oxides and near-neighbor group 5/group 6 results in higher activity toward water, while group 7/group 6 oxides form very specific stoichiometries that suggest facile regeneration. Studies on the trans-periodic combination of cerium oxide and platinum as a model for ceria supported Pt atoms and nanoparticles reveal striking negative charge accumulation by Pt, which, combined with the ionic conductivity of ceria, suggests a mechanism for the exceptionally high activity of this system towards the water-gas shift reaction.

Cr-Dopant Induced Breaking of Scaling Relations in CoFe Layered Double Hydroxides for Improvement of Oxygen Evolution Reaction

Monodentate adsorption of oxygen intermediates results in a theoretical overpotential limit of ≈0.35 V for oxygen evolution reaction (OER), which causes the sluggish kinetics of the OER process. In this work, nonprecious chromium dopant is introduced into the self-supported CoFe layered double hydroxides (LDHs) on nickel foam (Cr-CoFe LDHs/NF) via a facile one-step hydrothermal method, which exhibits a preeminent electrocatalytic activity toward the OER with an ultralow overpotential of 238 mV to obtain 10 mA cm^-2 and a high stability after cyclic voltammetry for 5000 cycles in alkaline solution (1 m KOH). Density functional theory (DFT) calculations unveil that Cr dopants as new active sites could improve the electron-donation ability of the resultant Cr-CoFe LDHs due to the smaller electronegativity of Cr in comparison with Fe and Co. Therefore, the scaling relation of adsorption energy among four oxygen intermediates is broken and consequently the OER performance is further promoted. This work provides a strategy to develop efficient metal layered double hydroxide OER catalysts.

Flexible vanadium-doped Ni2P nanosheet arrays grown on carbon cloth for an efficient hydrogen evolution reaction

Tuning the electronic structure, morphology, and structure of electrocatalysts is of great significance to achieve a highly active and stable hydrogen evolution reaction (HER). Herein, combining hydrothermal and low temperature phosphidation methods, V-doped Ni2P nanosheet arrays grown on carbon cloth (V-Ni2P NSAs/CC) were successfully prepared for the HER. It is found that the prepared V-Ni2P NSAs/CC exhibits preeminent performance for the HER. Specifically, it only requires an overpotential of 85 mV to achieve a current density of 10 mA cm-2 in 1.0 M KOH solution. Moreover, the V-Ni2P NSAs/CC shows superior electrochemical stability, maintaining its HER performance up to 3000 cyclic voltammetry cycles. This work affords a guiding strategy for the synthesis of a high-performance and stable electrocatalyst for the HER.