A two-dimensional MXene-supported metal-organic framework for highly selective ambient electrocatalytic nitrogen reduction.

The conversion of nitrogen into ammonia is crucial for human activities. The electrochemical synthesis of ammonia from nitrogen and water is a green process with great application prospects; to this end, much effort has been made to improve the catalytic activity and selectivity. Here, a Co-based metal-organic framework (MOF), that is, zeolitic imidazolate framework-67 (ZIF-67), supported on a Ti3C2 MXene (defined as ZIF-67@Ti3C2) was prepared via in situ growth. Due to the high porosity and large active surface area of the MOF and the superior conductivity of the Ti3C2 MXene, the composite could efficiently synthesize ammonia electrochemically. In particular, the prepared ZIF-67@Ti3C2 catalyst exhibited an excellent NH3 yield (6.52 µmol h-1 cm-2), significantly higher than those achieved by Ti3C2 and ZIF-67 (2.77 and 1.61 µmol h-1 cm-2, respectively) alone, and good Faraday efficiency (20.2%) at -0.4 V (vs. the reversible hydrogen electrode). This study not only expands the application of the MXene family in the electrochemical nitrogen reduction reaction but also provides ideas for the development of high-performance electrocatalysts for NRR.

Theoretical study of the influence of doped niobium on the electronic properties of CsPbBr3.

In the family of inorganic perovskite solar cells (PSCs), CsPbBr3 has attracted widespread attention due to its excellent stability under high humidity and high temperature conditions. However, power conversion efficiency (PCE) improvement of CsPbBr3-based PSCs is markedly limited by the large optical absorption loss coming from the wide band gap and serious charge recombination at interfaces and/or within the perovskite film. In this work, using density functional theory calculations, we systemically studied the electronic properties of niobium (Nb)-doped CsPbBr3 with different concentration ratios. As a result, it is found that doped CsPbBr3 compounds are metallic at high Nb doping concentration but semiconducting at low Nb doping concentration. The calculated electronic density of states shows that the conduction band is predominantly constructed of doped Nb. These characteristics make them very suitable for solar cell and energy storage applications.

Electrocatalytic Synthesis of Ammonia Using a 2D Ti3 C2 MXene Loaded with Copper Nanoparticles.

As an energy-saving and environmentally friendly ammonia synthesis method, electrocatalytic nitrogen reduction reaction (NRR) has received a great deal of attention. There is thus an urgent need to find high-efficiency electrocatalysts for the NRR. In this work, a Cu/Ti3 C2 composite catalyst was prepared and demonstrated excellent selectivity under environmental conditions, which could efficiently convert N2 into NH3 electrochemically. In 0.1 M KOH, Cu/Ti3 C2 can achieve a high Faradaic efficiency of 7.31 % and a high NH3 production rate of 3.04 µmol h-1 cm-2 at -0.5 V vs. RHE. Moreover, the material also exhibits superior electrochemical stability and durability. At the same time, density functional theory (DFT) shows that, compared with Ti3 C2 , Cu/Ti3 C2 exhibits a wider conduction and valence band and a larger Fermi level, thus indicating that Cu plays a vital role in the enhancement of the catalytic activity and conductivity of Ti3 C2 -based materials. This work provides a feasible strategy for designing high-efficiency MXene-based NRR electrocatalysts.

Current Progress of Electrocatalysts for Ammonia Synthesis Through Electrochemical Nitrogen Reduction Under Ambient Conditions.

Ammonia, one of the most important chemicals and carbon-free energy carriers, is mainly produced by the traditional Haber-Bosch process operated at high pressure and temperature, which results in massive energy consumption and CO2 emissions. Alternatively, the electrocatalytic nitrogen reduction reaction to synthesize NH3 under ambient conditions using renewable energy has recently attracted significant attention. However, the competing hydrogen evolution reaction (HER) significantly reduces the faradaic efficiency and NH3 production rate. The design of high-performance electrocatalysts with the suppression of the HER for N2 reduction to NH3 under ambient conditions is a crucial consideration for the development of electrocatalytic NH3 synthesis with high FE and NH3 production rate. Five kinds of recently developed electrocatalysts classified by their chemical compositions are summarized, with particular emphasis on the relationship between their optimal electrocatalytic conditions and NH3 production performance. Conclusions and perspectives are provided for the future design of high-performance electrocatalysts for electrocatalytic NH3 production. The Review can give practical guidance for the design of effective electrocatalysts with high FE and NH3 production rates.

A two-dimensional Ru@MXene catalyst for highly selective ambient electrocatalytic nitrogen reduction.

Compared with the traditional Haber-Bosch process, electrochemical ammonia synthesis has attracted much attention owing to its low energy consumption, low pollution potential, and sustainability. However, owing to the influence of high overpotential and low selectivity, the nitrogen reduction reaction (NRR) process was of limited applicability in industry. Here, we report a high-performance Ru@Ti3C2 MXene catalyst for an ambient electrocatalytic NRR. In a 0.1 M KOH electrolyte, the NH3 yield of the Ru@MXene catalyst reached 2.3 µmol h-1 cm-2, furthermore, at -0.4 V (vs. RHE) the Faraday efficiency was 13.13%.