Low-Pt NiNC-supported PtNi nanoalloy oxygen reduction reaction electrocatalysts—In situ tracking of the atomic alloying process

Carbon-supported platinum-nickel (Pt-Ni) alloy nanoparticles (NPs) emerge as the electrocatalysts of choice for deployment in polymer electrolyte membrane fuel cell (PEMFC) cathodes. To date, viable PtNi nanoalloy catalysts are characterized by large Pt weight loading of up to 50 wt%. To a large extent, their preparation processes often involve the use of expensive or even hazardous organometallic metal precursors, solvents and capping agents, substantially limiting their synthetic scalability and sustainability. Here, we report a novel synthetic strategy toward highly active low-Pt loaded PtNi nanoalloy Oxygen Reduction Reaction (ORR) catalysts. The synthesis involves the Pyrolysis and Leaching of Ni-organic polymers, subsequent Pt nanoparticle Deposition followed by thermal Alloying (referred to as PLDA) to prepare single Ni atom site (NiNC)-supported bimetallic PtNi nanoalloy electrocatalysts with very low Pt weight contents of 3–5 wt% Pt loading. We demonstrate that despite this low Pt weight loading, the catalysts exhibit more favorable Pt-mass activities compared to conventional, carbon-supported 20–30 wt%Pt Pt-loaded benchmark PtNi alloy catalysts. Using in situ transmission electron microscopy, cyclic voltammetry, and surface CO stripping techniques, we track and unravel the key stages of the formation process of the PtNi nanoparticle catalysts directly at the atomic scale. By carefully chosen reference experiments, we find that carbon-encapsulated Ni NPs, rather than NiNx single sites, serve exclusively as the Ni atom source for PtNi alloy formation during thermal treatments. Our materials concepts offer a pathway to further decrease the overall Pt content of PEM fuel cell devices.

Topology optimization of structures subject to self-weight loading under stress constraints

PurposeThe purpose of this paper is to present an approach for structural weight minimization under von Mises stress constraints and self-weight loading based on the topological derivative method. Although self-weight loading topology has been the subject of intense research, mainly compliance minimization has been addressed.Design/methodology/approachThe resulting minimization problem is solved with the help of the topological derivative method, which allows the development of efficient and robust topology optimization algorithms. Then, the derived result is used together with a level-set domain representation method to devise a topology design algorithm.FindingsNumerical examples are presented, showing the effectiveness of the proposed approach in solving a structural topology optimization problem under self-weight loading and stress constraint. When the self-weight loading is dominant, the presence of the regularizing term in the formulation is crucial for the design process.Originality/valueThe novelty of this research work lies in the use of a regularized formulation to deal with the presence of the self-weight loading combined with a penalization function to treat the von Mises stress constraint.

Systematic study of precursor effects on structure and oxygen reduction reaction activity of FeNC catalysts

In this work, the effect of porphyrin loading and template size is varied systematically to study its impact on the oxygen reduction reaction (ORR) activity and selectivity as followed by rotating ring disc electrode experiments in both acidic and alkaline electrolytes. The structural composition and morphology are investigated by 57 Fe Mössbauer spectroscopy, transmission electron microscopy, Raman spectroscopy and Brunauer–Emmett–Teller analysis. It is shown that with decreasing template size, specifically the ORR performance towards fuel cell application gets improved, while at constant area loading of the iron precursor (here expressed in number of porphyrin layers), the iron signature does not change much. Moreover, it is well illustrated that too large area loadings result in the formation of undesired side phases that also cause a decrease in the performance, specifically in acidic electrolyte. Thus, if the impact of morphology is the focus of research it is important to consider the area loading rather than its weight loading. At constant weight loading, beside morphology the structural composition can also change and impact the catalytic performance. This article is part of the theme issue ‘Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 2)’.

Steady Fluid–Structure Coupling Interface of Circular Membrane under Liquid Weight Loading: Closed-Form Solution for Differential-Integral Equations

In this paper, the problem of fluid–structure interaction of a circular membrane under liquid weight loading is formulated and is solved analytically. The circular membrane is initially flat and works as the bottom of a cylindrical cup or bucket. The initially flat circular membrane will undergo axisymmetric deformation and deflection after a certain amount of liquid is poured into the cylindrical cup. The amount of the liquid poured determines the deformation and deflection of the circular membrane, while in turn, the deformation and deflection of the circular membrane changes the shape and distribution of the liquid poured on the deformed and deflected circular membrane, resulting in the so-called fluid-structure interaction between liquid and membrane. For a given amount of liquid, the fluid-structure interaction will eventually reach a static equilibrium and the fluid-structure coupling interface is steady, resulting in a static problem of axisymmetric deformation and deflection of the circular membrane under the weight of given liquid. The established governing equations for the static problem contain both differential operation and integral operation and the power series method plays an irreplaceable role in solving the differential-integral equations. Finally, the closed-form solutions for stress and deflection are presented and are confirmed to be convergent by the numerical examples conducted.

Highly stretchable, non-flammable and notch-insensitive intrinsic self-healing solid-state polymer electrolyte for stable and safe flexible lithium batteries

A highly stretchable (extensibility > 4000% and stress > 130 kPa), adhesive (weight loading > 200 g), non-flammable and notch-insensitive intrinsic self-healing solid-state polymer electrolyte is designed for stable and safe flexible batteries.

Human Locomotion Strategies Under Changed Bodyweight Support

INTRODUCTION: The aim of this study was the analysis of human musculoskeletal system energy costs of normal walking and walking under reduced weight loading.METHODS: There were 15 subjects who participated in the study. We analyzed the biomechanical parameters of walking under different musculoskeletal system loads. The subjects walked on a treadmill at a pace of 90 steps/min under various loading conditions: 1) 100% bodyweight loading, corresponding to the terrestrial surface; 2) 38% bodyweight loading, corresponding to the surface of Mars; and 3) 17% bodyweight loading, corresponding to the surface of the Moon. Joint angles and angular velocities were recorded from the hip, knee, and ankle.RESULTS: We analyzed changes in joint phase trajectories and the ratio of kinetic extension energy to kinetic flexion energy in the joints. We observed changes in kinetic energy parameters associated with both flexion and extension motions in the joints of the feet while walking under various loads. In terrestrial conditions (walking under 100% bodyweight), flexion kinetic energy in the hip joint prevailed over extension kinetic energy by 90%, with a small variation equal to 22%. If weight loading decreased up to 17% (lunar conditions), the difference between flexion and extension kinetic energies diminished, and eventually reached only 9%. The ratio of flexion energy and extension energy in the ankle joint equalized under lower loading conditions. Thus, 38% bodyweight loading was sufficient for approximation of flexion and extension energy values.DISCUSSION: Our results revealed that phase trajectories shifted toward smaller joint angles and a decreased ratio between extension kinetic energy and flexion kinetic energy in the knee joint of all subjects. However, significant differences in the ratio of flexion and extension kinetic energy in the knee joint under bodyweight support were not found. The methods used for musculoskeletal system assessments that were proposed in our work can be used in clinical practice to evaluate the effectiveness of rehabilitation measures in a patients musculoskeletal system disorders.Shpakov AV, Artamonov AA, Voronov AV, Plotnikov EV, Puchkova AA, Orlov DO. Human locomotion strategies under changed bodyweight support. Aerosp Med Hum Perform. 2021; 92(1):410.