Synergic effect of Fe-doping and Ni3S2/MnS heterointerface to boost efficient oxygen evolution reaction

Co3S4/MnS p-p heterojunction as a highly efficient electrocatalyst for water splitting and electrochemical oxidation of organic molecules

In this work, Co3S4/MnS p-p heterojunction catalyst with hollow structure was successfully synthesized by one-step hydrothermal method. For oxygen evolution reaction (OER), urea oxidation reaction (UOR), lactate oxidation reaction (OER-LA) and glucose oxidation reaction (GOR), 1.59 V, 1.49 V, 1.54 V and 1.40 V vs. RHE are required to drive a current density of 50 mA cm-2, respectively, and the overpotential of hydrogen evolution reaction (HER) in 1 M KOH is 0.193 V at 50 mA cm-2. For the two-electrode overall water splitting in 1 M KOH, 1 M KOH containing 0.5 M urea, 1 M KOH containing 0.125 M lactate electrolyte and 1 M KOH containing 0.3 M glucose, water splitting voltages are only required at 1.73 V, 1.60 V, 1.62 V and 1.63 V to drive the current density of 50 mA cm-2. Moreover, its activity does not attenuate significantly in 1 M KOH containing 0.125 M lactate after continuous operation at 50 mA cm-2 for 200 h, showing excellent durability. In addition, the technology of glucose oxidation assisted water splitting for hydrogen production has been preliminarily explored, which also has excellent HER performance. Density functional theory (DFT) show that the p-p heterojunction between Co3S4 and MnS is conducive to the redistribution of electrons at the interface, thus promoting electron migration. Finally, the water splitting cell coupled with lactic acid oxidation reaction using polylactic acid pipette as source also exhibits high activity and stability. This study provides another idea and strategy for hydrogen production while waste plastic treatment.

MnS-BaS Heterostructures as Effective Catalysts for Oxygen Reduction Reaction

The inadequate electrical conductivity of metal sulfides, along with their tendency to agglomerate, has hindered their use in energy storage and catalysis. The construction of a heterojunction can ameliorate these deficiencies to some extent. In this paper, MnS-BaS heterojunction catalysts were prepared by a hydrothermal method, which is a simple and inexpensive process. The MnS-BaS heterojunction catalysts exhibited superior performance owing to the strong synergistic interaction between MnS and BaS. Density functional theory (DFT) calculations reveal strong interactions at the heterojunction interface and significant electron transfer between MnS and BaS, which further modulates the electronic structure of Mn. The elevation of the center of the d-band enhances the adsorption of oxygen and oxygen-containing intermediates on the catalyst, thus promoting the oxygen reduction reaction (ORR). The practical application of MnS-BaS catalysts was tested by assembling zinc-air batteries. This study provides a rational strategy for designing transition metal catalysts that are efficient and low cost.

High-performance spinel NiMn2O4 supported carbon felt for effective electrochemical conversion of ethylene glycol and hydrogen evolution applications

One of the most effective electrocatalysts for electrochemical oxidation reactions is NiMn2O4 spinel oxide. Here, a 3-D porous substrate with good conductivity called carbon felt (CF) is utilized. The composite of NiMn2O4-supported carbon felt was prepared using the facile hydrothermal method. The prepared electrode was characterized by various surface and bulk analyses like powder X-ray diffraction, X-ray photon spectroscopy (XPS), Scanning and transmitted electron microscopy, thermal analysis (DTA), energy dispersive X-ray (EDX), and Brunauer-Emmett-Teller (BET). The activity of NiMn2O4 toward the electrochemical conversion of ethylene glycol at a wide range of concentrations was investigated. The electrode showed a current density of 24 mA cm-2 at a potential of 0.5 V (vs. Ag/AgCl). Furthermore, the ability of the electrode toward hydrogen evaluation in an alkaline medium was performed. Thus, the electrode achieved a current density equal 10 mA cm-2 at an overpotential of 210 mV (vs. RHE), and the provided Tafel slope was 98 mV dec-1.

Nano-Scale Engineering of Heterojunction for Alkaline Water Electrolysis

Alkaline water electrolysis is promising for low-cost and scalable hydrogen production. Renewable energy-driven alkaline water electrolysis requires highly effective electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). However, the most active electrocatalysts show orders of magnitude lower performance in alkaline electrolytes than that in acidic ones. To improve such catalysts, heterojunction engineering has been exploited as the most efficient strategy to overcome the activity limitations of the single component in the catalyst. In this review, the basic knowledge of alkaline water electrolysis and the catalytic mechanisms of heterojunctions are introduced. In the HER mechanisms, the ensemble effect emphasizes the multi-sites of different components to accelerate the various intermedium reactions, while the electronic effect refers to the d-band center theory associated with the adsorption and desorption energies of the intermediate products and catalyst. For the OER with multi-electron transfer, a scaling relation was established: the free energy difference between HOO* and HO* is 3.2 eV, which can be overcome by electrocatalysts with heterojunctions. The development of electrocatalysts with heterojunctions are summarized. Typically, Ni(OH)2/Pt, Ni/NiN3 and MoP/MoS2 are HER electrocatalysts, while Ir/Co(OH)2, NiFe(OH)x/FeS and Co9S8/Ni3S2 are OER ones. Last but not the least, the trend of future research is discussed, from an industry perspective, in terms of decreasing the number of noble metals, achieving more stable heterojunctions for longer service, adopting new craft technologies such as 3D printing and exploring revolutionary alternate alkaline water electrolysis.

Recent Advances in Manganese-Based Materials for Electrolytic Water Splitting

Developing earth-abundant and highly effective electrocatalysts for electrocatalytic water splitting is a prerequisite for the upcoming hydrogen energy society. Recently, manganese-based materials have been one of the most promising candidates to replace noble metal catalysts due to their natural abundance, low cost, adjustable electronic properties, and excellent chemical stability. Although some achievements have been made in the past decades, their performance is still far lower than that of Pt. Therefore, further research is needed to improve the performance of manganese-based catalytic materials. In this review, we summarize the research progress on the application of manganese-based materials as catalysts for electrolytic water splitting. We first introduce the mechanism of electrocatalytic water decomposition using a manganese-based electrocatalyst. We then thoroughly discuss the optimization strategy used to enhance the catalytic activity of manganese-based electrocatalysts, including doping and defect engineering, interface engineering, and phase engineering. Finally, we present several future design opportunities for highly efficient manganese-based electrocatalysts.