3D printing of metal-based materials for renewable energy applications

Large-scale renewable energy must overcome conversion and storage challenges before it can replace fossil fuels due to its intermittent nature.However,current sustainable energy devices still suffer from high cost,low efficiency,and poor service life problems.Recently,porous metal-based materials have been widely used as desirable cross-functional platforms for electrochemical and photochemical energy systems for their unique electrical conductivity,catalytic activity,and chemical stability.To tailor the porosity length scale,ordering,and compositions,3D printing has been applied as a disruptive manufacturing revolution to create complex architected components by directly joining sequential layers into designed structures.This article intends to summarize cutting-edge advances of metal-based materials for renewable energy devices(e.g.,fuel cells,solar cells,supercapacitors,and batteries)over the past decade.

Monte Carlo Simulation of the Structure of Mono-and Bidisperse Polyethylene Nanocomposites

The structure of bidisperse polyethylene（PE） nanocomposite mixtures of 50：50（by mole） of long and short chains of C160H322/C80H162 and C160H322/C40H82 filled with spherical nanoparticles were investigated by a coarse-grained, on lattice Monte Carlo method using rotational isomeric state theory for short-range and Lennard-Jones for long-range energetic interactions. Simulations were performed to evaluate the effect of wall-to-wall distance between fillers（D）, polymer-filler interaction（w） and polydispersity（number of short chains in the mixture） on the behavior of the long PE chains. The results indicate that long chain conformation statistics remain Gaussian regardless of the effects of confinement, interaction strength and polydispersity. The various long PE subchain structures（bridges, dangling ends, trains, and loops） are influenced strongly by confinement whereas monomer-filler interaction and polydispersity did not have any impact. In addition, the average number of subchain segments per filler in bidisperse PE nanocomposites decreased by about 50% compared to the nanocomposite system with monodisperse PE chains. The presence of short PE chains in the polymer matrix leads to a reduction of the repeat unit density of long PE chains at the interface suggesting that the interface is preferentially populated by short chains.

Viscoelastic behavior of nanotube-filled polycarbonate:Effect of aspect ratio and interface chemistry

A combined experimental and modeling study on the solid-state rheology of multi-walled carbon nanotube(MWNT)/polycarbonate composites as a function,independently,of MWNT aspect ratio and interface chemistry was carried out.Shorter aspect ratio nanotubes lead to greater broadening of the loss modulus peak in frequency space,but there was no effect of aspect ratio on the glass transition temperature.The breadth of the loss modulus peak was found to correlate with the free space parameter,a measure of the spacing between the MWNTs.A new model that accounts for the aspect ratio and distribution in a representative volume element was developed to study these parameters in a controlled setting where morphology was precisely known.Micromechanics modeling was found to correlate well with experimental data.These results shed light on the separate impacts of aspect ratio,dispersion,and interface modification on the solid-state rheology of nanofilled polymers.

Single asperity friction in the wear regime

We used molecular dynamics simulation to investigate the friction of a single asperity against a rigid substrate, while generating debris. In the low wear regime(i.e., non-linear wear rate dependence on the contact stress, via atom-by-atom attrition), the frictional stress is linearly dependent on the normal stress, without any lubrication effect from the wear debris particles. Both the slope(friction coefficient) and friction at zero normal stress depend strongly on asperity-substrate adhesion. In the high wear regime(i.e., linear wear rate dependence on the contact stress, via plastic flow), the friction-normal stress curves deviate from a linear relation merging toward plastic flow of the single asperity which is independent of the interfacial adhesion. One can further link wear and friction by considering debris generation as chemical reaction, driven by both normal and frictional forces. The coupling between wear and friction can then be quantified by a thermodynamic efficiency of the debris generation. While the efficiency is less than 5% in the low wear regime, indicating poor mechanochemical coupling, it increases with normal stress toward 50% in the high wear regime.