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The development of highly efficient, stable, and low-cost electrocatalysts for oxygen evolution reaction (OER) is crucial for enhancing the efficiency of water splitting, but it still remains a huge challenge. Herein, three-dimensional (3D) self-supported Cr-doped Ni3N (Cr–Ni3N) nanosheet arrays were synthesized successfully on the carbon cloth by the hydrothermal method and subsequent nitridation process. Cr–Ni3N displays a superior alkaline OER performance with a low overpotential of 290 mV at the current density of 50 mA cm–2, a small Tafel slope of 56 mV dec–1, and robust electrochemical stability, which is much better than those of bare Ni3N and commercial RuO2. The calculation of density functional theory reveals that electron-rich Cr atoms transfer electrons to electron-deficient Ni and N atoms, effectively adjust the surface electron configuration of the Cr–Ni3N catalyst, and optimize the H2O adsorption in the 1 M KOH solution during the OER process. Additionally, the partially oxidized Cr6+ during the OER can optimize the electronic structure and enhance the stability of NiOOH active sites by the strong electron withdrawing ability. This work can provide a pathway to rationally design efficient transition metal nitride-based OER electrocatalysts. [ABSTRACT FROM AUTHOR]

As a common smart hydrogel, thermo‐sensitive hydrogel exhibits significant potential applications in the field of biological engineering due to its unique property of undergoing a substantial volume transition in response to temperature changes. For numerical implementation of thermo‐sensitive hydrogel, many approaches have been developed to simulate the transient deformation during fluid diffusion or heat conduction process. However, the numerical approach for the transient deformation during both fluid diffusion and heat conduction processes is still lacking. To this end, we develop a three‐field coupled finite element framework that can be used to simulate the transient deformation behavior of thermo‐sensitive hydrogel involving large deformation, fluid diffusion, and heat conduction. In the proposed framework, there exist three processes that deal with displacement, concentration, and temperature fields, separately. To realize the coupling of three fields, the separated solving processes are assembled together by using a two‐way coupled approach. Based on the developed finite element framework, the coupling effects between the concentration and temperature can be realized by defining a body flux and a temperature‐dependent diffusion coefficient without solving the complex coupling equations. The finite element framework is implemented in ABAQUS by utilizing several user subroutines. The numerical implementation is validated by comparing the numerical results of a hydrogel disk with experimental results. Furthermore, various numerical examples are simulated to investigate the applicability of the proposed finite element framework under different multi‐field coupling conditions. The proposed finite element scheme is proved to be an efficient and stable tool for numerically simulating the transient behavior of thermo‐sensitive hydrogel incorporating the phase transition effect. [ABSTRACT FROM AUTHOR]

This paper proposes novel unit cells that can be arranged periodically constructing disparate auxetic metamaterials with negative Poisson's ratio for engineering applications. The two-dimensional auxetic unit cells are designed utilizing the mathematical model of the modified Solid Isotropic Material with Penalization (SIMP) topological optimization method with the objective of maximizing the magnitude of the negative Poisson's ratio. The deformation mechanisms of the auxetic structures are controlled effectively by straight and oblique struts attached at rotation joints since the optimum designs are a combination of chiral and re-entrant unit cells. Three structures with optimum auxetic designs are chosen to verify the modified SIMP method using numerical simulation. Additionally, the energy absorption and vibration mitigation of auxetic metamaterials have been extensively studied. The results showed a significant impact of negative Poisson's ratio on the considered dynamic properties of the auxetic structures. [ABSTRACT FROM AUTHOR]

This work presents a network mechanics method to reveal the fracture mechanism of the inhomogeneous polymer network of elastomers. The polymer network in elastomers is abstracted as a network model composed of cross-linkers, polymer chains, and volume elements. The hyperelastic deformation of the network model is characterized using the total energy composed by the free energy of all polymer chains and the volumetric deformation energy of all volume elements. The fracture behavior of the network model is described by the fracture criterion of polymer chains. By comparing the large-deformation fracture simulations of homogeneous and inhomogeneous network models, we find that the network inhomogeneity is one important fundamental cause of the ductile fracture and the low notch sensitivity of elastomers. We also find that the widely used Lake–Thomas model underestimates the intrinsic fracture energy of elastomers, because the intrinsic fracture energy of an elastomer network includes the elastic energy stored not only in the broken polymer chains, but also in the newly created dangling chains on a crack surface. Our simulations show that the intrinsic fracture energy of a four-armed elastomer network is about three times of that predicted by the Lake–Thomas model. This result agrees quite well with the previous experimental results. [ABSTRACT FROM AUTHOR]