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Herein, we present the investigation of catalytical and fluorescence properties for Ni11(HPO3)8(OH)6 materials obtained through a hydrothermal approach. As part of the constant search for new materials that are both cost effective and electrocatalytically active for the oxygen evolution reaction (OER) in alkaline medium, the present study involves several graphite electrodes modified with Ni11(HPO3)8(OH)6 mixed with reduced graphene oxide (rGO) and carbon black. The experimental results obtained in 0.1 mol L–1 KOH electrolyte solution show the electrode modified with rGO, 5 mg carbon black and 1 mg nickel phosphite as displaying the highest current density. This performance can be attributed to the synergistic effect between nickel phosphite and the carbon materials. Investigation of the electrode's OER performance in 0.1 mol L–1 KOH solution revealed a Tafel slope value of just 46 mV dec–1. By increasing the concentration to 0.5 and 1 mol L–1, this value increased as well, but there was a significant decrease in overpotential. Fluorescence properties were analyzed for the first time at the excitation length of 344 nm, and the observed strong and multiple emissions are described. [ABSTRACT FROM AUTHOR]

In this research paper, the thermal behaviour of the mixed valence iron oxides Fe3(PO4)2(OH)2 is presented in both air and vacuum atmosphere. The structure, morphology and the magnetic properties of the iron phosphates samples obtained at selected temperatures were carefully investigated. The electrocatalytic properties of synthetic barbosalite Fe3(PO4)2(OH)2 materials for the oxygen and hydrogen evolution reactions (OER and HER) were investigated in a wide pH range, using graphite electrodes modified with different compositions containing the catalyst. The best results were obtained for the compositions with 6 mg barbosalite. During the HER experiments, overpotentials of − 300 and − 350 mV were observed at the current density of − 10 mA cm−2 in strong alkaline and in strong acidic media, respectively. During the OER studies performed in strong acidic solution and in neutral environment, overpotentials of 320 and 690 mV were obtained at the current density of 10 mA cm−2. These findings complement the existing scientific literature relevant to the water splitting domain. Furthermore, the visible light absorption ability of synthetic Fe2+Fe3+2(PO4)2(OH)2 materials was also evaluated. [ABSTRACT FROM AUTHOR]

Present day scientific research is focused on the identification of renewable and clean alternatives to fossil fuels, with hydrogen being a promising energy source that fulfills both requirements. Given this context, the current work investigates the water splitting electrocatalytic properties of two hydrothermally synthesized transition metal oxides: MnO2 and Fe3O4. Electrodes were obtained by modifying graphite substrates with suspensions in ethanol containing the catalytic materials as such or in compositions, and their activity for the O2 and H2 evolution reactions (OER and HER) was studied in alkaline medium. Out of the MnO2-based electrodes, the one modified with the suspension containing 2 mg MnO2, 1 mg Carbon Black and 10 μL Nafion solution displayed an OER overpotential (ηO2) value, at i = 10 mA/cm2, of 0.53 V, while the one manufactured using the suspension with 4 mg MnO2 and 10 μL Nafion solution showed a HER overpotential (ηH2) of 0.427 V (at i = -10 mA/cm2). From the Fe3O4-based electrodes, the one modified with the suspension containing 2 mg Fe3O4 and 2 mg Carbon Black evidenced the highest catalytic activity for both reactions (ηO2 = 0.51 V and ηH2 = 0.43 V). [ABSTRACT FROM AUTHOR]

Ni 11□ (HPO 3) 8 (OH) 6 nanorods were the focus of three different studies. First, the thermal behaviour of the material was investigated and it outlined a good thermal stability up to 400 °C. Second, a comparative electrochemical study concerning the OER performance in alkaline medium of several graphite electrodes modified with the nickel phosphite was performed. The most promising electrodes were further characterised electrochemically and the electrode modified with Nafion solution and 5 mg Ni 11□ (HPO 3) 8 (OH) 6 exhibited the smallest overpotential value at the 10 mA cm−2 anodic current density (0.59 V), as well as the smallest Tafel slope (0.081 V dec−1). Furthermore, the constant potential electrolysis test revealed that this electrode is fairly stable within a time span of 300 min. Third, the capacity of Ni 11□ (HPO 3) 8 (OH) 6 nanorods to remove MB and RhB were investigated under simulated visible light irradiation and positive results were obtained for the application as visible-light active photocatalyst. All this together corroborated with the eco-friendly nature of the materials, reinforces the fact that the phosphite type compound is a promising candidate for the design of new multifunctional and advanced materials. • Ni 11□ (HPO 3) 8 (OH) 6 acts as OER catalyst in alkaline medium. • Positive results were obtained for application as visible-light active photocatalyst. • Ni 11□ (HPO 3) 8 (OH) 6 has a good thermal stability in air up to 400 °C. [ABSTRACT FROM AUTHOR]