Hierarchical sheet-on-sheet heterojunction array of a β-Ni(OH)2/Fe(OH)3 self-supporting anode for effective overall alkaline water splitting

Co-Removal of Fe/V Impurity in H2TiO3 Synthesized from Ti-Bearing Blast Furnace Slag

Ti-bearing blast furnace slag (TBFS) can be converted to impurity bearing TiOSO4 solution for TiO2 pigment production. However, the H2TiO3 (MTA) hydrolyzed from the solution has too high Fe/V impurity to meet the standard for TiO2 pigment. In this study, we found that Fe3+ and V3+ were easily hydrolyzed and entered the MTA lattice, and hence could not be removed by washing. Furthermore, Fe/V was hard to co-remove by the traditional reduction method. Therefore, the Fe/V non-hydrolysis condition (Ti3+ = 0.01 M, F = 3.0, T = 130 °C; Ti3+ = 0.01 M, F = 3.5, T = 150 °C) was determined by thermodynamic calculations. However, at these conditions, the Ti hydrolysis ratio was low or the reaction time was long. Therefore, a new two-step hydrothermal hydrolysis process was proposed. Step 1 (130 °C, 2 h) ensured the non-hydrolysis of V3+, and Ti was partially hydrolyzed to increase the H2SO4 concentration. Step 2 (150 °C, 2 h) ensured a high Ti hydrolysis ratio (>0.95) and short total reaction time (4-6 h). Finally, a high-purity MTA was obtained (Fe = 21 ppm, V = 145 ppm). These results provide new insights into the control of the hydrolysis of impurity ions in solutions and help to optimize the process of TiO2 pigment preparation from TBFS.

Synergistic coupling of heterostructured porous CoP nanosheets with P doped NiO for highly efficient overall alkaline water splitting

Exploring non-noble metal materials as bifunctional catalysts for water electrolysis is of great significance for the development and utilization of hydrogen energy. Herein, a flower branch-leaf shaped phosphide/oxide heterogeneous electrocatalyst located on Ni foam (CoP/P-NiO/NF) was developed through hydrothermal and phosphorization strategy. Benefiting from the strong ability to dissociate H₂O molecules on P-NiO and the suitable adsorption of intermediate H species on CoP, the optimal CoP/P-NiO/NF exhibited outstanding performance with low overpotentials of 52 mV at current density of 10 mA cm^-2, smaller Tafel slopes of 73.6 mV dec^-1 for hydrogen evolution reaction (HER). Meanwhile, CoP/P-NiO/NF indicated 265 mV at 100 mA cm^-2 with Tafel slope of 101.8 mV dec^-1 for oxygen evolution reaction (OER) due to the optimal redistribution of electrons among Ni²⁺, Co²⁺ and Co³⁺ for favorable adsorption/desorption of oxygen-intermediates. Both HER and OER shown robust stability during 32 h without decline. The corresponding two-electrode system for overall alkaline water splitting required a low voltage of 1.6 V at 100 mA cm^-2 with long stability (20 h) which is far lower than that on RuO₂-Pt/C and many other reported non-noble metal electrocatalysts. This work demonstrates that the synergistic effect and morphology engineering play vital roles in the enhanced electrocatalytic performance.

Influence of Fe-clustering on the water oxidation performance of two-dimensional layered double hydroxides

Among the two-dimensional (2D) materials family, layered double hydroxides (LDHs) represent a key member due to their unparalleled chemical versatility. In particular, Fe-based LDHs are distinguished candidates due to their high efficiency as oxygen evolution reaction (OER) electrocatalysts. Herein, we have selected MgFe-based LDH phases as model systems in order to decipher whether Fe-clustering exerts an effect on the OER performance. For that, we have optimized hydrothermal synthesis by using triethanolamine (TEA) as the chelating agent. The magnetic characterisation allows us to identify the Fe-clustering degree by following both magnetic susceptibility as well as magnetization values at 2 K. Thanks to this, we demonstrated that TEA induces an increment in Fe-clustering. Electrochemical OER measurements show that both samples behave identically by using glassy carbon electrodes. Interestingly, when the samples are tested in the most commonly employed electrode, nickel foam, striking differences arise. The sample exhibiting a lower Fe-clustering behaves as a better electrocatalyst with a reduction of the overpotential values of more than 50 mV to reach 100 mA cm^-2, as a consequence of a favoured surface transformation of MgFe-LDHs phases into more reactive oxyhydroxide NiFe-based phases during the electrochemical tests. Hence, this work alerts about the importance of the electrocatalyst-electrode collector interactions which can induce misinterpretations in the OER performance.