Fuel-Driven Redox Reactions in Electrolyte-Free Polymer Actuators for Soft Robotics

Polymers that undergo shape changes in response to external stimuli can serve as actuators and offer significant potential in a variety of technologies, including biomimetic artificial muscles and soft robotics. Current polymer artificial muscles possess major challenges for various applications as they often require extreme and non-practical actuation conditions. Thus, exploring actuators with new or underutilized stimuli may broaden the application of polymer-based artificial muscles. Here, we introduce an all-solid fuel-powered actuator that contracts and expands when exposed to H2 and O2 via redox reactions. This actuator demonstrates a fully reversible actuation magnitude of up to 3.8% and achieves a work capacity of 120 J/kg. Unlike traditional chemical actuators, our actuator eliminates the need for electrolytes, electrodes, and the application of external voltage. Moreover, it offers athermal actuation by avoiding the drawbacks of thermal actuators. Remarkably, the actuator maintains its actuated position under load when not stimulated, without consuming energy (i.e., catch state). These fuel-powered fiber actuators were embedded in a soft humanoid hand to demonstrate finger-bending motions. In terms of two main actuation metrics, stress-free contraction strain and blocking stress, the presented artificial muscle outperforms reported polymer redox actuators. The fuel-powered actuator developed in this work creates new avenues for the application of redox polymers in soft robotics and artificial muscles.

Lattice Strain and Surface Activity of Ternary Nanoalloys under the Propane Oxidation Condition

The ability to harness the catalytic oxidation of hydrocarbons is critical for both clean energy production and air pollutant elimination, which requires a detailed understanding of the dynamic role of the nanophase structure and surface reactivity under the reaction conditions. We report here findings of an in situ/operando study of such details of a ternary nanoalloy under the propane oxidation condition using high-energy synchrotron X-ray diffraction coupled to atomic pair distribution function (HE-XRD/PDF) analysis and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The catalysts are derived by alloying Pt with different combinations of second (Pd) and third (Ni) transition metals, showing a strong dependence of the catalytic activity on the Ni content. The evolution of the phase structure of the nanoalloy is characterized by HE-XRD/PDF probing of the lattice strain, whereas the surface activity is monitored by DRIFTS detection of the surface intermediate formation during the oxidation of propane by oxygen. The results reveal the dominance of the surface intermediate species featuring a lower degree of oxygenation upon the first C-C bond cleavage on the lower-Ni-content nanoalloy and a higher degree of oxygenation upon the second C-C bond cleavage on the higher-Ni-content nanoalloy. The face-centered-cubic-type phase structures of the nanoalloys under the oxidation condition are shown to exhibit Ni-content-dependent changes of lattice strains, featuring the strongest strain with little variation for the higher-Ni-content nanoalloy, in contrast to the weaker strains with oscillatory variation for the lower-Ni-content nanoalloys. This process is also accompanied by oxygenation of the metal components in the nanoalloy, showing a higher degree of oxygenation for the higher-Ni-content nanoalloy. These subtle differences in phase structure and surface activity changes correlate with the Ni-composition-dependent catalytic activity of the nanoalloys, which sheds a fresh light on the correlation between the dynamic change of atomic strains and the surface reactivity and has significant implications for the design of oxidation catalysts with enhanced activities.

Vapor-fed bio-hybrid fuel cell

BACKGROUND

Concentration and purification of ethanol and other biofuels from fermentations are energy-intensive processes, with amplified costs at smaller scales. To circumvent the need for these processes, and to potentially reduce transportation costs as well, we have previously investigated bio-hybrid fuel cells (FCs), in which a fermentation and FC are closely coupled. However, long-term operation requires strictly preventing the fermentation and FC from harming each other. We introduce here the concept of the vapor-fed bio-hybrid FC as a means of continuously extracting power from ongoing fermentations at ambient conditions. By bubbling a carrier gas (N₂) through a yeast fermentation and then through a direct ethanol FC, we protect the FC anode from the catalyst poisons in the fermentation (which are non-volatile), and also protect the yeast from harmful FC products (notably acetic acid) and from build-up of ethanol.

RESULTS

Since vapor-fed direct ethanol FCs at ambient conditions have never been systematically characterized (in contrast to vapor-fed direct methanol FCs), we first assess the effects on output power and conversion efficiency of ethanol concentration, vapor flow rate, and FC voltage. The results fit a continuous stirred-tank reactor model. Over a wide range of ethanol partial pressures (2-8 mmHg), power densities are comparable to those for liquid-fed direct ethanol FCs at the same temperature, with power densities >2 mW/cm² obtained. We then demonstrate the continuous operation of a vapor-fed bio-hybrid FC with fermentation for 5 months, with no indication of performance degradation due to poisoning (of either the FC or the fermentation). It is further shown that the system is stable, recovering quickly from disturbances or from interruptions in maintenance.

CONCLUSIONS

The vapor-fed bio-hybrid FC enables extraction of power from dilute bio-ethanol streams without costly concentration and purification steps. The concept should be scalable to both large and small operations and should be generalizable to other biofuels and waste-to-energy systems.

Simple, fast, and accurate methodology for quantitative analysis using Fourier transform infrared spectroscopy, with bio-hybrid fuel cell examples

The standard methodologies for quantitative analysis (QA) of mixtures using Fourier transform infrared (FTIR) instruments have evolved until they are now more complicated than necessary for many users’ purposes. We present a simpler methodology, suitable for widespread adoption of FTIR QA as a standard laboratory technique across disciplines by occasional users.•

Algorithm is straightforward and intuitive, yet it is also fast, accurate, and robust.

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Relies on component spectra, minimization of errors, and local adaptive mesh refinement.

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Tested successfully on real mixtures of up to nine components.

We show that our methodology is robust to challenging experimental conditions such as similar substances, component percentages differing by three orders of magnitude, and imperfect (noisy) spectra. As examples, we analyze biological, chemical, and physical aspects of bio-hybrid fuel cells.

Aspergillus oryzae-Saccharomyces cerevisiae Consortium Allows Bio-Hybrid Fuel Cell to Run on Complex Carbohydrates

Consortia of Aspergillus oryzae and Saccharomyces cerevisiae are examined for their abilities to turn complex carbohydrates into ethanol. To understand the interactions between microorganisms in consortia, Fourier-transform infrared spectroscopy is used to follow the concentrations of various metabolites such as sugars (e.g., glucose, maltose), longer chain carbohydrates, and ethanol to optimize consortia conditions for the production of ethanol. It is shown that with proper design A. oryzae can digest food waste simulants into soluble sugars that S. cerevisiae can ferment into ethanol. Depending on the substrate and conditions used, concentrations of 13% ethanol were achieved in 10 days. It is further shown that a direct alcohol fuel cell (FC) can be coupled with these A. oryzae-enabled S. cerevisiae fermentations using a reverse osmosis membrane. This “bio-hybrid FC” continually extracted ethanol from an ongoing consortium, enhancing ethanol production and allowing the bio-hybrid FC to run for at least one week. Obtained bio-hybrid FC currents were comparable to those from pure ethanol—water mixtures, using the same FC. The A. oryzae–S. cerevisiae consortium, coupled to a bio-hybrid FC, converted food waste simulants into electricity without any pre- or post-processing.

Excited-state absorption of a bipyridyl platinum(II) complex with alkynyl-benzothiazolylfluorene units

The singlet excited-state lifetime of a bipyridyl platinum(II) complex containing two alkynyl-benzothiazolylfluorene units was determined to be 145+/-105 ps by fitting femtosecond transient difference absorption data, and the triplet quantum yield was measured to be 0.14. A ground-state absorption cross section of 6.1 x 10(-19) cm(2) at 532 nm was deduced from UV-visible absorption data. Excited-state absorption cross sections of (6.7+/-0.1) x 10(-17) cm(2) (singlet) and (4.6+/-0.1) x 10(-16) cm(2) (triplet) were obtained by using a five-level dynamic model to fit open-aperture Z scans at picosecond and nanosecond pulse widths and a variety of pulse energies. For this complex, the ratio of the triplet excited-state absorption cross section to the ground-state absorption cross section--long used as a figure of merit for reverse saturable absorbers--thus stands at 754, to our knowledge the largest ever reported at 532 nm wavelength.

Multimode interference devices with input-output ports on the sides

Multimode interference (MMI) devices are useful for power splitting and for the separation or combination of wavelengths or polarizations, usually in integrated optics. Input-output guides connect to the MMI region by ports. In all previously reported MMI devices, the input and output guides connect only to the ends of the MMI region; i.e., they are end ported. What is believed to be a novel arrangement of the input-output ports on MMI devices is described. By placing input-output ports either partially or entirely on the sides of the MMI region (i.e., side porting), a variety of benefits are achieved and a variety of new devices can be made.

Slotted multimode-interference devices

We describe a novel modification of multimode-interference devices that has broad applicability. The modification involves introducing a slot (or slots), of a specific width and effective refractive index and at a specific position, that runs the longitudinal length of the multimode-interference region. Introducing N slots reduces the self-image length by a factor of N + 1. Varying the effective refractive index or width of the slot(s) creates a switch. The slot modification can be accomplished in a variety of ways, actually increases bandwidth, and has good error tolerances.

Preoptimization improvements to subwavelength diffractive lenses

We present preoptimization strategies for improving the design of diffractive lenses in the electromagnetic domain, with few or no electromagnetic analyses. We find that improvements can be substantial, in some cases even to the point that extensive electromagnetic optimization gives only marginal additional improvement.

Intergroup emotions: explaining offensive action tendencies in an intergroup context

Three studies tested the idea that when social identity is salient, group-based appraisals elicit specific emotions and action tendencies toward out-groups. Participants' group memberships were made salient and the collective support apparently enjoyed by the in-group was measured or manipulated. The authors then measured anger and fear (Studies 1 and 2) and anger and contempt (Study 3), as well as the desire to move against or away from the out-group. Intergroup anger was distinct from intergroup fear, and the inclination to act against the out-group was distinct from the tendency to move away from it. Participants who perceived the in-group as strong were more likely to experience anger toward the out-group and to desire to take action against it. The effects of perceived in-group strength on offensive action tendencies were mediated by anger.

The impact of stereotype-incongruent information on perceived group variability and stereotype change

Three experiments showed increases in the perceived variability of social groups after perceivers received stereotype-incongruent information about group members. In Experiment 1, participants generated flatter distributions after exposure to incongruent information, compared with equally deviant congruent information, in the form of typical verbal materials. Experiment 2 indicated similar changes in dispersion after the presentation of numeric information about a single group member. In Experiment 3, the authors manipulated cognitive load at encoding or at the time group judgments were requested. Under conditions of cognitive constraint, stereotype-incongruent information ceased to promote more dispersed group representations. These results are consistent with the idea that incongruent information triggers more deliberative and comprehensive retrieval and generation of exemplars. The authors discuss the implications of these findings for stereotype change.

The impact of stereotype-incongruent information on perceived group variability and stereotype change

Three experiments showed increases in the perceived variability of social groups after perceivers received stereotype-incongruent information about group members. In Experiment 1, participants generated flatter distributions after exposure to incongruent information, compared with equally deviant congruent information, in the form of typical verbal materials. Experiment 2 indicated similar changes in dispersion after the presentation of numeric information about a single group member. In Experiment 3, the authors manipulated cognitive load at encoding or at the time group judgments were requested. Under conditions of cognitive constraint, stereotype-incongruent information ceased to promote more dispersed group representations. These results are consistent with the idea that incongruent information triggers more deliberative and comprehensive retrieval and generation of exemplars. The authors discuss the implications of these findings for stereotype change.

Intergroup relations: insights from a theoretically integrative approach

In social psychology, specific research traditions, which often spring up in response to external events or social problems, tend to perpetuate the theoretical assumptions and methodological approaches with which they began. As a result, theories and methods that have proven powerful in 1 topic area are often not applied in other areas, even to conceptually similar issues. The authors adopt a theoretically integrative approach to the topic of intergroup relations. Theories and empirical approaches from the domains of attitudes, impression formation, the self, personal relationships, and norms offer many new insights into problematic issues, such as repeated findings of dissociations among stereotyping, prejudice, and discrimination. This integrative approach not only promises new theoretical advances, but also suggests numerous potential practical approaches to limiting or reducing destructive patterns of intergroup relations.

Mood effects on attitude judgments: independent effects of mood before and after message elaboration

This study investigated the independent effects of induced mood on the encoding of persuasive messages and on the assessment of attitude judgments. In Experiment 1, positive or negative mood was induced either before the encoding of a counterattitudinal message or before the assessment of attitude judgments. When mood was induced before message presentation, Ss in a bad mood were more persuaded by strong than by weak arguments, whereas Ss in a good mood were equally persuaded by strong and by weak arguments. When Ss encoded the message in a neutral mood, however, the advantage of strong over weak arguments was more pronounced when Ss were in a good rather than in a bad mood at the time of attitude assessment. In Experiment 2, Ss exposed to a counterattitudinal message composed of either strong or weak arguments formed either a global evaluation or a detailed representation of the message. Positive, negative, or neutral mood was then induced. Ss in a good mood were most likely and Ss in a negative mood least likely to base their reported attitudes on global evaluations.

Affect and stereotyping: the effect of induced mood on distinctiveness-based illusory correlations

In 2 studies, the effects of mood on the formation of distinctiveness-based illusory correlations were examined. After exposure to stimuli inducing positive, neutral, or negative mood, Ss read information about behaviors performed by members of 2 groups in an illusory correlation paradigm. In both experiments, only Ss in a neutral mood formed illusory correlations. In addition, Experiment 2 assessed Ss' processing latencies as a means of investigating differential attention to distinctive behaviors. Only Ss in a neutral mood differentially attended to the minority group's infrequent behaviors. Induced mood apparently interfered with the processing necessary to differentially encode distinctive stimuli, undermining the illusory correlation effect.

Mood effects on attitude judgments: Independent effects of mood before and after message elaboration

This study investigated the independent effects of induced mood on the encoding of persuasive messages and on the assessment of attitude judgments. In Experiment 1, positive or negative mood was induced either before the encoding of a counterattitudinal message or before the assessment of attitude judgments. When mood was induced before message presentation, Ss in a bad mood were more persuaded by strong than by weak arguments, whereas Ss in a good mood were equally persuaded by strong and by weak arguments. When Ss encoded the message in a neutral mood, however, the advantage of strong over weak arguments was more pronounced when Ss were in a good rather than in a bad mood at the time of attitude assessment. In Experiment 2, Ss exposed to a counterattitudinal message composed of either strong or weak arguments formed either a global evaluation or a detailed representation of the message. Positive, negative, or neutral mood was then induced. Ss in a good mood were most likely and Ss in a negative mood least likely to base their reported attitudes on global evaluations.

Affect and stereotyping: The effect of induced mood on distinctiveness-based illusory correlations

In 2 studies, the effects of mood on the formation of distinctiveness-based illusory correlations were examined. After exposure to stimuli inducing positive, neutral, or negative mood, Ss read information about behaviors performed by members of 2 groups in an illusory correlation paradigm. In both experiments, only Ss in a neutral mood formed illusory correlations. In addition, Experiment 2 assessed Ss' processing latencies as a means of investigating differential attention to distinctive behaviors. Only Ss in a neutral mood differentially attended to the minority group's infrequent behaviors. Induced mood apparently interfered with the processing necessary to differentially encode distinctive stimuli, undermining the illusory correlation effect.

On-line and memory-based modification of attitudes: determinants of message recall-attitude change correspondence

Experiments investigated the impact of message elaboration on attitude change-message recall correspondence when attitude change occurs in an on-line (as attitude-relevant information is received), or memory-based (on the basis of retrieved attitude-relevant information) fashion. In 2 experiments, Ss' processing goals were manipulated to increase or inhibit on-line change and message elaboration. As predicted, Ss reported postexposure attitudes more rapidly in on-line vs memory-based conditions. Decreased message elaboration increased attitude-recall correspondence, regardless of when attitude change occurred. Increased elaboration produced elaboration-attitude judgment correspondence. Results suggest that recall of message content will best predict persuasion when message content is encoded free of elaborations, regardless of when attitude change occurs.

Processing of persuasive in-group messages

Two studies investigated the processes mediating the persuasive impact of messages representing in-group opinions. In the 1st study, subjects read either a strong or a weak message attributed to either an in-group member or to another group. Subjects were more persuaded by a strong message from the in-group than a weak one, suggesting content-focused processing of the in-group message. Subjects were equally unpersuaded by either a strong or a weak message from the other group, and showed little sign of message processing. In the 2nd study, Ss listened to in-group or other-group messages about issues that varied in their relevance to in-group membership. When the issue was relevant to the in-group, subjects were persuaded by a strong message from the in-group, unpersuaded by a weak message from the in-group, and equally unimpressed by strong and weak messages from the other group. When the issue was irrelevant to the in-group, subjects accepted the position advocated by the in-group regardless of message quality, and again ignored messages from the other group. These results suggest that increased message processing, and not merely the impact of source persuasion cues, can underlie in-group-mediated attitude change.

On-line and memory-based modification of attitudes: Determinants of message recall-attitude change correspondence

Experiments investigated the impact of message elaboration on attitude change-message recall correspondence when attitude change occurs in an on-line (as attitude-relevant information is received), or memory-based (on the basis of retrieved attitude-relevant information) fashion. In 2 experiments, Ss' processing goals were manipulated to increase or inhibit on-line change and message elaboration. As predicted, Ss reported postexposure attitudes more rapidly in on-line vs memory-based conditions. Decreased message elaboration increased attitude-recall correspondence, regardless of when attitude change occurred. Increased elaboration produced elaboration-attitude judgment correspondence. Results suggest that recall of message content will best predict persuasion when message content is encoded free of elaborations, regardless of when attitude change occurs.

Processing of persuasive in-group messages

Two studies investigated the processes mediating the persuasive impact of messages representing in-group opinions. In the 1st study, subjects read either a strong or a weak message attributed to either an in-group member or to another group. Subjects were more persuaded by a strong message from the in-group than a weak one, suggesting content-focused processing of the in-group message. Subjects were equally unpersuaded by either a strong or a weak message from the other group, and showed little sign of message processing. In the 2nd study, Ss listened to in-group or other-group messages about issues that varied in their relevance to in-group membership. When the issue was relevant to the in-group, subjects were persuaded by a strong message from the in-group, unpersuaded by a weak message from the in-group, and equally unimpressed by strong and weak messages from the other group. When the issue was irrelevant to the in-group, subjects accepted the position advocated by the in-group regardless of message quality, and again ignored messages from the other group. These results suggest that increased message processing, and not merely the impact of source persuasion cues, can underlie in-group-mediated attitude change.

Processing deficits and the mediation of positive affect in persuasion

Motivational and cognitive mediators of the reduced processing of persuasive messages shown by recipients in a positive mood were tested. Ss in positive or neutral moods read strong or weak counterattitudinal advocadies for either a limited time or for as long as they wanted. Under limited exposure conditions, neutral mood Ss showed attitude change indicative of systemic processing, whereas positive mood Ss showed no differentiation of strong and weak versions of the message. When message exposure was unlimited, positive mood Ss viewed the message longer than did neutral mood Ss and systematically processed it rather than relying on persuasion heuristics. These findings replicated with 2 manipulations of mood and 2 different attitude issues. We interpret the results as providing evidence that reduced cognitive capacity to process the message contributes to the decrements shown by positive mood Ss.

Processing deficits and the mediation of positive affect in persuasion

Motivational and cognitive mediators of the reduced processing of persuasive messages shown by recipients in a positive mood were tested. Ss in positive or neutral moods read strong or weak counterattitudinal advocadies for either a limited time or for as long as they wanted. Under limited exposure conditions, neutral mood Ss showed attitude change indicative of systemic processing, whereas positive mood Ss showed no differentiation of strong and weak versions of the message. When message exposure was unlimited, positive mood Ss viewed the message longer than did neutral mood Ss and systematically processed it rather than relying on persuasion heuristics. These findings replicated with 2 manipulations of mood and 2 different attitude issues. We interpret the results as providing evidence that reduced cognitive capacity to process the message contributes to the decrements shown by positive mood Ss.