Nanoarchitecture materials are widely investigated to enhance hydrogen evolution reaction (HER) performance. However, it is beset with difficulties to obtain nanomaterials at industrial-scale in comparison with bulk materials. Herein, bulk electrocatalyst Fe 4.5 Ni 4.5 S 8 /Fe 7 S 8 is prepared using flotation method and alkali cleaning from natural nickel ore. Sulfur vacancies and electron interaction between Fe 7 S 8 and Fe 4.5 Ni 4.5 S 8 may efficiently reduce hydrogen adsorption energy's absolute value, thus significantly improving hydrogen production efficiency. Hybrid catalyst requires ultralow overpotential of 48 mV at 10 mA cm −2 for HER in 0.5 M H 2 SO 4 and exhibits high stability (maintaining an almost constant overpotential after 20,000 cyclic voltammetry sweeps). Therefore, it can be affirmed that it demonstrates promising industrial application as an electrocatalyst towards HER.
Partial neutralization is typically used to remove Fe 3+ ions from the acid leach solution of laterite. However, during this process, significant amounts of Mg 2+ , Ni 2+ , Co 2+ , and SO 2– 4 are lost. With increasing initial Fe 3+ concentration and solution pH, the severity of loss increases, with the precipitation of Fe 3+ . In this study, the mechanisms of ion co-precipitation during partial neutralization were investigated. Based on density functional theory calculations, a precipitation pathway through the formation of [Fe 4 (OH − ) 2 (SO 2– 4) 4 ]•[2SO 2 – 4 •yH 2 O]•[M 2+ ] was proposed. The differential charge density diagram indicated that the O atoms acted as the charge acceptors and maintained the precipitate structure. The coordination between M 2+ and SO 2– 4 could be destroyed via intense agitation, releasing approximately 100% of Mg 2+ , Ni 2+ , and Co 2+ ions from the precipitates to the solution. Furthermore, the addition of cationic or anionic surfactants limited the formation of these coordination bonds. The highest retention percentages of Mg 2+ , Ni 2+ , and Co 2+ in solution were 99.4, 99.6, and 99.9%, respectively, after adding 2 × 10 −5 mol/L of sodium dodecylbenzenesulfonate (CTAB). In addition, a high temperature could break these coordination bonds. The retention percentages of Mg 2+ , Ni 2+ , and Co 2+ increased from 82.6, 85.2, and 86.5% to 99.9, 99.6, and 99.8%, respectively, as the temperature increased from 25 to 65 °C. These results confirmed the rationality of the proposed structure of the precipitate.
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