Doping of Cr to Regulate the Valence State of Cu and Co Contributes to Efficient Water Splitting.

Water electrolysis in alkaline media is the most promising technology for hydrogen production, but efficient electrocatalysts are required to reduce the overpotential in HER and OER processes. In this work, the multicomponent transition metal catalyst Cr-Cu/CoOx was loaded on copper foam by electrodeposition and annealing, and the catalyst exhibited excellent electrochemical activity. The HER overpotential is 21 mV and the OER overpotential is 252 mV at a current density of 10 mA cm-2. The overall water splitting voltage is 1.51 V, even better than the Pt/C//RuO2 two-electrode system (1.61 V). The excellent performance of this catalyst is mainly derived from the close synergistic interaction among Cu, Co, and Cr. The doping of Cr modulates the valence states of Cu and Co at the active sites and improves the adsorption of various reaction intermediates. Density functional theory (DFT) calculations show that the doping of Cr can optimize the adsorption of the reaction intermediate H*. Meanwhile, the high-valent Cr and Co promote hydrolysis through strong adsorption with OH-. The present work provides a reasonable strategy for designing low-cost transition metals as efficient catalysts for water electrolysis.

A survey of caregiver burden for stroke survivors in non-teaching hospitals in Western China.

The social factors that moderate stroke caregiver burden have been found to be culture- and gender-specific. We examined the factors that influence the social support and self-efficacy of caregivers of stroke survivors and the burden of caregiving in China. To determine the caregiver burden of stroke survivors, their social support, and their self-efficacy. A total of 328 stroke survivors and their caregivers were recruited from 4 tertiary medical centers to participate in this cross-sectional study. The sociodemographic and stroke-related characteristics of the participants were obtained. Perceived social support and self-efficacy were assessed using the Social Support Rating Scale and General Self-efficacy Scale, respectively. Caregiver burden was assessed using the Zarit Burden Interview Scale. Relationships between the variables were assessed using Pearson's correlation, the chi-square test, and a paired t test. A total of 27.4% of the caregivers reported receiving adequate social support, while 20.7% reported high levels of self-efficacy. A total of 67.1% of the caregivers experienced varying degrees of care burden, while the remaining 32.9% felt no burden. Participants' sociodemographic characteristics (age, daily care time, self-rated health, and financial situation) were significantly related to caregiver burden, social support, and self-efficacy (P < .001). The findings indicate an inverse relationship between caregiver burden, social support and self-efficacy. Adequate social support and self-efficacy can reduce stroke caregivers' burden. Hospital departments should provide assistance to stroke caregivers through educational programs and group training to increase their social support and self-efficacy, thereby alleviating their burden.

Origami by frontal photopolymerization.

Origami structures are of great interest in microelectronics, soft actuators, mechanical metamaterials, and biomedical devices. Current methods of fabricating origami structures still have several limitations, such as complex material systems or tedious processing steps. We present a simple approach for creating three-dimensional (3D) origami structures by the frontal photopolymerization method, which can be easily implemented by using a commercial projector. The concept of our method is based on the volume shrinkage during photopolymerization. By adding photoabsorbers into the polymer resin, an attenuated light field is created and leads to a nonuniform curing along the thickness direction. The layer directly exposed to light cures faster than the next layer; this nonuniform curing degree leads to nonuniform curing-induced volume shrinkage. This further introduces a nonuniform stress field, which drives the film to bend toward the newly formed side. The degree of bending can be controlled by adjusting the gray scale and the irradiation time, an easy approach for creating origami structures. The behavior is examined both experimentally and theoretically. Two methods are also proposed to create different types of 3D origami structures.

Desolvation Induced Origami of Photocurable Polymers by Digit Light Processing.

Self-folding origami is of great interest in current research on functional materials and structures, but there is still a challenge to develop a simple method to create freestanding, reversible, and complex origami structures. This communication provides a feasible solution to this challenge by developing a method based on the digit light processing technique and desolvation-induced self-folding. In this new method, flat polymer sheets can be cured by a light field from a commercial projector with varying intensity, and the self-folding process is triggered by desolvation in water. Folded origami structures can be recovered once immersed in the swelling medium. The self-folding process is investigated both experimentally and theoretically. Diverse 3D origami shapes are demonstrated. This method can be used for responsive actuators and the fabrication of 3D electronic devices.

Effects of oxygen on light activation in covalent adaptable network polymers.

Light activated polymers are a novel group of active materials that deform when irradiated with light at specific wavelengths. This paper focuses on the understanding and evaluation of light activated covalent adaptable networks formed by radical polymerization reactions, which have potential applications as novel actuators, surface patterning, and light-induced bending and folding. In these polymer networks, free radicals are generated upon light irradiation and lead to evolution of the polymer network structure through bond exchange reactions. It is well known that oxygen is an important inhibitor in radical-based chemistry as oxygen reacts with free radicals and renders them as inactive species towards further propagation and reaction. However, it is unclear how radical depletion by oxygen may affect the light-induced actuation. This paper studies the effects of oxygen on both stress relaxation and bending actuation. Light induced stress relaxation experiments are conducted in an environmental chamber where the concentration of oxygen is controlled by the nitrogen flow. A constitutive model that considers oxygen diffusion, radical termination due to oxygen, and the polymer network evolution is developed and used to study the stress relaxation and bending, and the model predictions agree well with experiments. Parametric studies are conducted to identify the situations where the effects of oxygen are negligible and other conditions where they must be considered.

A molecular dynamics study of bond exchange reactions in covalent adaptable networks.

Covalent adaptable networks are polymers that can alter the arrangement of network connections by bond exchange reactions where an active unit attaches to an existing bond then kicks off its pre-existing peer to form a new bond. When the polymer is stretched, bond exchange reactions lead to stress relaxation and plastic deformation, or the so-called reforming. In addition, two pieces of polymers can be rejoined together without introducing additional monomers or chemicals on the interface, enabling welding and reprocessing. Although covalent adaptable networks have been researched extensively in the past, knowledge about the macromolecular level network alternations is limited. In this study, molecular dynamics simulations are used to investigate the macromolecular details of bond exchange reactions in a recently reported epoxy system. An algorithm for bond exchange reactions is first developed and applied to study a crosslinking network formed by epoxy resin DGEBA with the crosslinking agent tricarballylic acid. The trace of the active units is tracked to show the migration of these units within the network. Network properties, such as the distance between two neighboring crosslink sites, the chain angle, and the initial modulus, are examined after each iteration of the bond exchange reactions to provide detailed information about how material behaviors and macromolecular structure evolve. Stress relaxation simulations are also conducted. It is found that even though bond exchange reactions change the macroscopic shape of the network, microscopic network characteristic features, such as the distance between two neighboring crosslink sites and the chain angle, relax back to the unstretched isotropic state. Comparison with a recent scaling theory also shows good agreement.

Photo-induced bending in a light-activated polymer laminated composite.

Light activated polymers (LAPs) have attracted increasing attention since these materials change their shape and/or behavior in response to light exposure, which serves as an instant, remote and precisely controllable stimulus that enables non-contact control of the material shape and behavior through simple variation in light intensity, wavelength and spatially controlled exposure. These features distinguish LAPs from other active polymers triggered by other stimuli such as heat, electrical field or humidity. Previous examples have resulted in demonstrations in applications such as surface patterning, photo-induced shape memory behavior, and photo-origami. However, in many of these applications, an undesirable limitation has been the requirement to apply and maintain an external load during light irradiation. In this paper, a laminated structure is introduced to provide a pre-programmed stress field, which is then used for photo-induced deformation. This laminated structure is fabricated by bonding a stretched elastomer (NOA65) sheet between two LAP layers. Releasing the elastomer causes contraction and introduces a compressive stress in the LAPs, which are relaxed optically to trigger the desired deformation. A theoretical model is developed to quantitatively examine the laminated composite system, allowing exploration of the design space and optimum design of the laminate.