Shape-programmable matter is a class of active materials whose geometry can be controlled to potentially achieve mechanical functionalities beyond those of traditional machines. Among these materials, magnetically actuated matter is particularly promising for achieving complex time-varying shapes at small scale (overall dimensions smaller than 1 cm). However, previous work can only program these materials for limited applications, as they rely solely on human intuition to approximate the required magnetization profile and actuating magnetic fields for their materials. Here, we propose a universal programming methodology that can automatically generate the required magnetization profile and actuating fields for soft matter to achieve new time-varying shapes. The universality of the proposed method can therefore inspire a vast number of miniature soft devices that are critical in robotics, smart engineering surfaces and materials, and biomedical devices. Our proposed method includes theoretical formulations, computational strategies, and fabrication procedures for programming magnetic soft matter. The presented theory and computational method are universal for programming 2D or 3D time-varying shapes, whereas the fabrication technique is generic only for creating planar beams. Based on the proposed programming method, we created a jellyfish-like robot, a spermatozoid-like undulating swimmer, and an artificial cilium that could mimic the complex beating patterns of its biological counterpart.programmable matter | multifunctional materials | soft robots | magnetic actuation | miniature devices S hape-programmable matter refers to active materials that can be controlled by heat (1-5), light (6, 7), chemicals (8-13), pressure (14, 15), electric fields (16, 17), or magnetic fields (18-33) to generate desired folding or bending. As these materials can reshape their geometries to achieve desired time-varying shapes, they have the potential to create mechanical functionalities beyond those of traditional machines (1, 15). The functionalities of shape-programmable materials are especially appealing for miniature devices whose overall dimensions are smaller than 1 cm as these materials could significantly augment their locomotion and manipulation capabilities. The development of highly functional miniature devices is enticing because, despite having only simple rigid-body motions (34-36) and gripping capabilities (37), existing miniature devices have already been used across a wide range of applications pertaining to microfluidics (38, 39), microfactories (40, 41), bioengineering (42, 43), and health care (35, 44).Among shape-programmable matter, the magnetically actuated materials are particularly promising for creating complex timevarying shapes at small scales because their control inputs, in the form of magnetic fields, can be specified not only in magnitude but also in their direction and spatial gradients. Furthermore, as they can be fabricated with a continuum magnetization profile, m, along their bodies, these magne...

Cobalt-containing spinel oxides are promising electrocatalysts for the oxygen evolution reaction (OER) owing to their remarkable activity and durability. However, the activity still needs further improvement and related fundamentals remain untouched. The fact that spinel oxides tend to form cation deficiencies can differentiate their electrocatalysis from other oxide materials, for example, the most studied oxygen-deficient perovskites. Here, a systematic study of spinel ZnFe Co O oxides (x = 0-2.0) toward the OER is presented and a highly active catalyst superior to benchmark IrO is developed. The distinctive OER activity is found to be dominated by the metal-oxygen covalency and an enlarged CoO covalency by 10-30 at% Fe substitution is responsible for the activity enhancement. While the pH-dependent OER activity of ZnFe Co O (the optimal one) indicates decoupled proton-electron transfers during the OER, the involvement of lattice oxygen is not considered as a favorable route because of the downshifted O p-band center relative to Fermi level governed by the spinel's cation deficient nature.

LaCoO 3 is an active, stable catalyst in alkaline solution for oxygen evolution reaction (OER). With lower cost, it is a potential alternative to precious metal oxides like IrO 2 and RuO 2 in water electrolysis. However, room still remains for improving its activity according to recent understandings of OER on perovskite oxides. In this work, Fe substitution has been introduced in LaCoO 3 to boost its OER performance. Density function theory (DFT) calculation verified that the enhanced performance originates from the enhanced Co 3d-O 2p covalency with 10 at% Fe substitution in LaCoO 3 . Both DFT calculations and Superconducting Quantum Design (SQUID) magnetometer (MPMS-XL) showed a Co 3+ spin state transition from generally low spin state (LS: t 2g 6 e g 0 , S = 0) to a higher spin state with the effect of 10 at% Fe substitution. X-ray absorption near-edge structure (XANES) supports DFT calculations on an insulator to half-metal transition with 10 at% Fe substitution, induced by spin state transition. The half-metallic LaCo 0.9 Fe 0.1 O 3 possesses increased overlap between Co 3d and O 2p states, which results in enhanced covalency and promoted OER performance. This finding enlightens a new way of tuning the metal−oxygen covalency in oxide catalysts for OER.

Cobalt spinel oxides are ac lass of promising transition metal (TM) oxides for catalyzing oxygen evolution reaction (OER). Their catalytic activity depends on the electronic structure.I naspinel oxide lattice,e acho xygen anion is shared amongst its four nearest transition metal cations,ofwhich one is located within the tetrahedral interstices and the remaining three cations are in the octahedral interstices. This work uncovered the influence of oxygen anion charge distribution on the electronic structure of the redox-active building blockC o ÀO. The charge of oxygen anion tends to shift toward the octahedral-occupied Co instead of tetrahedraloccupied Co,w hich hence produces strong orbital interaction between octahedral Co and O. Thus,t he OER activity can be promoted by pushing more Co into the octahedral site or shifting the oxygen charge towards the redox-active metal center in CoO 6 octahedra.The clean-burning hydrogen fuel, if produced by electrochemical water splitting, would revolutionize the global energy infrastructure.T he major limitation of water splitting is the sluggish oxygen evolution reaction (OER) at the anode. [1] To date,the most efficient OER electrocatalysts are made from noble metal ruthenium or iridium. In order to meet the broader goal of sustainability,e xploring earthabundant transition metal (TM) oxide catalysts have been prioritized. [1b, 2] Better understanding of the OER reaction on TM oxides is necessary to this end. It has been found that the surface redox-active centers in TM oxides play ak ey role in oxygen electrocatalysis. [3] Thec onventional perception of oxygen evolution regards the redox-active metallic center as the active site and it is the redox ability of TM that mediates the transition of [M n+ ÀOH ad ]/[M n+1 ÀO ad ]d uring OER. [3,4] However,t he redox of late transition metal oxides (e.g., Coand Ni-based) could involve both the transition metal and oxygen ligand due to the increased orbital hybridization between TM 3d and O2 p. [2,5] Earlier reports had demonstrated that the energy in TM 3d orbital cannot be treated in isolation from O2pwhen there is significant overlap between TM 3d and O2 p. Recent studies on oxygen-deficient perovskite oxides reveal that the oxygen anion could also act as the redox partner in OER. [6] Direct evidence for lattice oxygen participated OER using in situ 18 Oi sotope labelling mass spectrometry has been given by Alexis et al. [6b] Thefact that the oxygen anion can also act as the redox-active center emphasizes the importance of considering TM À Obond as the redox-active building block. More recently,t he covalent character (covalency) of TM Bs ite ÀOb ond (TM B the TM in B site) has been proposed to be adominating factor in OER on perovskite oxides. [6b, 7] TheA -site rare-earth metals (low in electronegativity) tend to form an ionic bond with Oa nd weaken the influence of M A -O block on OER. Spinel oxides, ah uge crystal family for oxygen electrocatalysis, [2,4,8] require more complex analysis because the tetrahedral and octahe...

electrolyzer are oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. The OER at the anode, proceeding through 4e − transfer and generates more than one intermediates, is much more kinetically sluggish than the 2e − transfer HER. [1] Lowering the energy barrier of OER is the key to the enhancement of overall water splitting efficiency. The state-of-the-art OER electrocatalysts, such as iridium-and ruthenium-based materials, are not sustainable choices due to the high cost and element scarcity. Transition metal (TM) oxides, with wide variety of physical and electronic properties, are considered as promising low-cost alternatives. [2] Spinel-type oxides have been extensively investigated as OER electrocatalysts and have presented outstanding catalytic performances. [2b,3] The crystal structure of spinel is made up of oxygen anions arranged in a cubic close-packed lattice with metallic ions filling the tetrahedral and octahedral interstices. Of all the 96 interstices between the oxygen anions in one cubic unit cell, 64 are four oxygencoordinated tetrahedral sites and 32 are six oxygen-coordinated octahedral sites. In the spinel lattice, only half of the octahedral interstices and one-eighth of the tetrahedral interstices are filled with metal cations. The remaining unoccupied interstitial sites make spinel a very open structure to accommodate the migration of cations. [4] For binary spinel AB 2 O 4 , the distribution of The clean energy carrier, hydrogen, if efficiently produced by water electrolysis using renewable energy input, would revolutionize the energy landscape. It is the sluggish oxygen evolution reaction (OER) at the anode of water electrolyzer that limits the overall efficiency. The large spinel oxide family is widely studied due to their low cost and promising OER activity. As the distribution of transition metal (TM) cations in octahedral and tetrahedral site is an important variable controlling the electronic structure of spinel oxides, the TM geometric effect on OER is discussed. The dominant role of octahedral sites is found experimentally and explained by computational studies. The redox-active TM locating at octahedral site guarantees an effective interaction with the oxygen at OER conditions. In addition, the adjacent octahedral centers in spinel act cooperatively in promoting the fast OER kinetics. In remarkable contrast, the isolated tetrahedral TM centers in spinel prohibit the OER mediated by dual-metal sites. Furthermore, various spinel oxides preferentially expose octahedral-occupied cations on the surface, making the octahedral cations easily accessible to the reactants. The future perspectives and challenges in advancing fundamental understanding and developing robust spinel catalysts are discussed.

When a thin film of active, nematic microtubules and kinesin motor clusters is confined on the surface of a vesicle, four +1/2 topological defects oscillate in a periodic manner between tetrahedral and planar arrangements. Here a theoretical description of nematics, coupled to the relevant hydrodynamic equations, is presented here to explain the dynamics of active nematic shells. In extensile microtubule systems, the defects repel each other due to elasticity, and their collective motion leads to closed trajectories along the edges of a cube. That motion is accompanied by oscillations of their velocities, and the emergence and annihilation of vortices. When the activity increases, the system enters a chaotic regime. In contrast, for contractile systems, which are representative of some bacterial suspensions, a hitherto unknown static structure is predicted, where pairs of defects attract each other and flows arise spontaneously.

Chiral nematic liquid crystals are known to form blue phases—liquid states of matter that exhibit ordered cubic arrangements of topological defects. Blue-phase specimens, however, are generally polycrystalline, consisting of randomly oriented domains that limit their performance in applications. A strategy that relies on nano-patterned substrates is presented here for preparation of stable, macroscopic single-crystal blue-phase materials. Different template designs are conceived to exert control over different planes of the blue-phase lattice orientation with respect to the underlying substrate. Experiments are then used to demonstrate that it is indeed possible to create stable single-crystal blue-phase domains with the desired orientation over large regions. These results provide a potential avenue to fully exploit the electro-optical properties of blue phases, which have been hindered by the existence of grain boundaries.

No abstract