Recent progress on control strategies for inherent issues in friction stir welding

The electrochemical nitrogen reduction reaction (NRR) is a very efficient method for sustainable NH3 production, but it requires effective catalysts to expedite the NRR kinetics and inhibit the con...

Two-dimensional (2D)/2D Interface Engineering of a MoS2/C3N4 Heterostructure for Promoted Electrocatalytic Nitrogen Fixation

Electrocatalytic conversion of N2 to NH3via the N2 reduction reaction (NRR) provides a sustainable avenue for large-scale NH3 production. However, it remains challenging to develop effective and durable NRR catalysts to promote the NH3 synthesis rate and faradaic efficiency (FE). Here, combining theoretical predictions and experimental verifications, we showed that the CoO nanostructures could be a new class of highly efficient NRR catalysts. Density functional theory calculations revealed that CoO possessed poor HER activity but favorable NRR activity. When supporting CoO quantum dots (QDs, 2–5 nm) on reduced graphene oxide (RGO), the resulting CoO QD/RGO exhibited a high NH3 yield of 21.5 μg h−1 mg−1 and an FE of 8.3% at −0.6 V vs. the reversible hydrogen electrode under ambient conditions, superior to most of the reported NRR catalysts. Furthermore, the CoO QD/RGO showed excellent selectivity and stability, demonstrating the great potential of Co-based catalysts for electrocatalytic synthesis of NH3.

Efficient electrocatalytic N2 reduction on CoO quantum dots

Electrocatalytic N2 reduction reaction (NRR) represents a sustainable and promising technology for producing NH3 at ambient conditions. Herein, we demonstrated that Mo-doping could change the MnO2 from an inert material into one that can efficiently and robustly catalyze NRR in neutral media. The developed Mo-doped MnO2 nanoflowers (Mo-MnO2 NFs) exhibited a significantly enhanced NRR performance with an NH3 yield of 36.6 μg h−1 mg−1 (-0.5 V) and an FE of 12.1 % (-0.4 V), far outperforming undoped MnO2 NFs and comparing favorably to most reported NRR catalysts. Density functional theory calculations revealed the electron-deficient character of Mo dopants that delivered multi-functions for NRR enhancement: (1) inducing a defect level to promote the conductivity of MnO2, (2) serving as the key NRR active sites, (3) activating the inert Mn sites for enhancing the intrinsic NRR activity of MnO2, (4) retarding the binding of Lewis acid H+ to suppress the hydrogen evolution reaction.

Multi-functional Mo-doping in MnO2 nanoflowers toward efficient and robust electrocatalytic nitrogen fixation

Mo2C nanoparticles grown on reduced graphene oxide (Mo2C@RGO) were used to prepare the Mo2C@RGO/Cu composite. The Mo2C nanoparticles played a bridging role in not only being firmly attached on RGO but also forming a semi-coherent interface with the Cu matrix, leading to strong interfacial bonding of the composites. The 1 vol% Mo2C@RGO/Cu composite exhibited a yield strength of 238 MPa, 58% and 127% higher than that of 1 vol% RGO/Cu composite and pure Cu, respectively. The strengthening mechanism of Mo2C@RGO/Cu composite relied on the dual role of Mo2C nanoparticles that not only enhanced the load transfer strengthening of RGO but also provided the possible Orowan strengthening themselves. Nevertheless, the Mo2C@RGO/Cu composite showed a drop in coefficient of thermal expansion but a reduced thermal conductivity compared to pure Cu and the RGO/Cu composite. This study provides new insights into the interface structure, strengthening mechanism and thermal behavior of carbide-modified graphene/metal composites.

Interface and mechanical/thermal properties of graphene/copper composite with Mo2C nanoparticles grown on graphene

Largely enhanced thermal conductivity of graphene/copper composites with highly aligned graphene network

Interface design of graphene/copper composites by matrix alloying with titanium

Interface structure and strengthening behavior of graphene/CuCr composites

The isotropic mechanical properties of graphene/metal composites with randomly distributed graphene have been extensively studied. However, the anisotropic mechanical properties of aligned graphene/metal composites in both in-plane and through-plane directions have not yet been reported. Herein, we attempted to align graphene nanoplatelets (GNPs) in the Cu matrix via a vacuum filtration method followed by spark plasma sintering. It was demonstrated that a fairly good GNP alignment was achieved in the composites, leading to the prominent anisotropic mechanical properties with in-plane tensile strength and elongation significantly outperforming through-plane ones. Nevertheless, only moderate in-plane strength enhancement (26% at 10 vol% GNPs) was obtained in the composites, and this enhancement was further diminished to −7.1% with increasing GNP fraction to 20 vol%, which was attributed primarily to the weak GNP-Cu interface that is bonded by mechanical interlocking. Furthermore, the anisotropic mechanical behavior of aligned GNP/Cu composites was proposed to originate from the different interface failure modes of 'GNP slippage' and 'GNP peer-off' with the load parallel and perpendicular to the alignment direction, respectively. Therefore, further improvement of interfacial bonding strength will be an important step towards the optimization of the anisotropic mechanical properties of aligned graphene/metal composites.

Fan Wang

Papers

Largely enhanced thermal conductivity of graphene/copper composites with highly aligned graphene network

Interface design of graphene/copper composites by matrix alloying with titanium

Interface and mechanical/thermal properties of graphene/copper composite with Mo2C nanoparticles grown on graphene

Interface structure and strengthening behavior of graphene/CuCr composites

Anisotropic mechanical properties of graphene/copper composites with aligned graphene