Atomic battery | EPFL Graph Search

An atomic battery, nuclear battery, radioisotope battery or radioisotope generator is a device which uses energy from the decay of a radioactive isotope to generate electricity. Like nuclear reactors, they generate electricity from nuclear energy, but differ in that they do not use a chain reaction. Although commonly called batteries, they are technically not electrochemical and cannot be charged or recharged. They are very costly, but have an extremely long life and high energy density, and so they are typically used as power sources for equipment that must operate unattended for long periods of time, such as spacecraft, pacemakers, underwater systems and automated scientific stations in remote parts of the world. Nuclear battery technology began in 1913, when Henry Moseley first demonstrated a current generated by charged particle radiation. The field received considerable in-depth research attention for applications requiring long-life power sources for space needs during the 19

Atomic Level Insights of Non-Noble Metal Catalysts for the Oxygen Evolution Reaction

Lichen Bai

The conversion of intermittent renewable energy resources in the form of chemical bond, such as hydrogen production from electrochemical water splitting, is a promising way to satisfy the future global energy demand and address the environmental issues. The oxygen evolution reaction (OER) is the bottleneck among the overall reaction due to its endergonic thermodynamics and complicated 4H+/4e- transfer process. Despite extensive efforts have been made to develop cheap, efficient and robust heterogeneous electrocatalysts for OER, their heterogeneous nature makes the deep investigation of the active sites and reaction mechanisms challenging. Benefiting from high atomic efficiency, excellent intrinsic activity, and well-defined active motifs, the atomically dispersed catalysts provides an opportunity to get insight of the catalysts. The Chapter 2 demonstrates a Co single-atom precatalyst immobilized on N-doped carbon support (Co-N-C) can be transformed to a Co-Fe double-atom catalyst (Co-Fe-N-C) via electrochemical activation in KOH containing Fe impurities. The Co-Fe-N-C exhibited a turnover frequency among one of the highest values of the state-of-the-art OER catalysts. Electrochemical, microscopic, and spectroscopic data, including atomic-resolution electron microscopy and operando X-ray absorption spectroscopy (XAS), reveal an atomically dispersed dimeric Co-Fe moiety as the active site of the Co-Fe-N-C. On the basis of Co-Fe-N-C, the Chapter 3 further describes a general synthesis of Co, Fe, and Ni-containing double-atom catalysts from their single-atom precursors via in situ electrochemical transformation. All these double-atom catalysts have molecule-like bimetallic active sites, which resembles the possible key active centers of bimetallic heterogeneous catalysts. In Chapter 4, a systematic mechanistic insight of the double-atom catalysts and the catalytic process were provided, by combining both electrokinetics analysis and operando XAS results. These mechanisms follow a similar O-O bond forming step and all exhibit bimetallic cooperation, while each mechanisms diverge in the catalytic site and the source of OH- for O-O bond formation as well as the order of proton and electron transfer. The works from Chapter 2-4 suggested that the double-atom catalysts not only provide an attractive molecular platform for fundamental studies of heterogeneous OER electrocatalysts, but also establish a bridge between homogeneous and heterogeneous OER catalysis. The traditional OER catalysts typically occurs via a mechanism involving four consecutive proton-coupled electron transfer (PCET) steps, which has a performance limit imposed by the scaling relationship of various oxygen intermediates. The Chapter 5 describes using operando Raman spectroscopy and electrokinetic analysis to study two active model OER catalysts, FeOOH-NiOOH composite and NiFe layered double hydroxide (LDH). The data that FeOOH-NiOOH operates by a bifunctional mechanism where the rate-determining O-O bond forming step is the OH- attack on a Fe=O coupled with a hydrogen atom transfer to a nearby NiIII-O site, whereas NiFe LDH operates by a conventional mechanism of four consecutive PCET steps. The bifunctional mechanism, hitherto only supported by theoretical computations, has the potential to circumvent the scaling relationship limit of conventional OER mechanism. Thus, this work provides the first experimental evidences to validate such novel mechanisms.

EPFL2021

Anchoring single platinum atoms onto nickel nanoparticles affords highly selective catalysts for lignin conversion

Lichen Bai, Lu Chen, Paul Joseph Dyson, Zhaofu Fei, Ulf Anders Hagfeldt, Gabor Laurenczy, Jun Li, Linfeng Pan, Yun Tong, Antoine Philippe Van Muyden

Due to the highly complex polyphenolic structure of lignin, depolymerization without a prior chemical treatment is challenging, and new catalysts are required. Atomically dispersed catalysts are able to maximize the atomic efficiency of noble metals, simultaneously providing an alternative strategy to tune the activity and selectivity by alloying with other abundant metal supports. Here, we report a highly active and selective catalyst comprising monodispersed (single) Pt atoms on Ni nanoparticles supported on carbon (denoted as Pt1Ni/C, where Pt-1 represents single Pt atoms), designed for the reductive depolymerization of lignin. Selectivity toward 4-n-propylsyringol and 4-n-propylguaiacol exceeds 90%. The activity and selectivity of the Pt1Ni/C catalyst in the reductive depolymerization of lignin may be attributed to synergistic effects between the Ni nanoparticles and the single Pt atoms.

ELSEVIER2021

Internal electric fields and electrode effects in ferroelectric thin films for piezoelectric energy harvesting

Robin Nigon

The continuing decrease of power requirements of electronic circuits offers the potential to deploy wireless systems as embedded sensors for cars or industrial tools, and implanted medical devices. Harvesting ambient vibrations by an appropriate energy harvesting (EH) device allows to avoid an undesirable battery replacement. At the scale of micro-electromechanical systems, where severe size constraints must be met, microfabricated EH devices with piezoelectric thin films offer the best energy density. Ferroelectric lead zirconate titanate (PZT) thin films with interdigitated electrodes (IDE) appear as the most promising device design for this purpose. Accurate characterization of the thin film response is necessary to determine the PZT composition and doping, the electrode geometry, and the stack design for maximum EH efficiency. Unfortunately, there is no rigorous description of the physical behavior of the IDE system to date. One goal of this thesis was thus to provide a better understanding of the experimental observations made by previous researchers. In addition, only a limited PZT composition and doping range has been investigated in this configuration. It was the second goal of this thesis to widen this range in order to determine the combination that yields the best EH efficiency. Finally, the risk of partial or total depoling over the device lifetime is always present in ferroelectric materials. The phenomena of aging and self-poling are of great interest to ensure proper retention of the poled state and, thus, the reliability of the harvesting device. Neither of the two are well understood. It was the third goal of this thesis to investigate the aging behavior and methods to promote self-poling. In this thesis work, we have have proposed a description of the physical behavior of the IDE system, and we have developed an analytical model for extracting the effective material properties from standard characterization measurements, which is well supported by both finite element (FE) simulations and experimental data. We found that if the substrate is conductive enough, a parasitic capacitance is present in parallel to the material response. We have provided a method to subtract the contribution of the parasitic capacitance, which has an accuracy of better than 4% in a wide range of IDE geometries as determined by FE simulations. We have investigated the performances of doped PZT thin films with IDE for several combinations of dopant and composition. We have improved an existing fabrication route to obtain textured PZT films on an insulating MgO layer. We found that dopants systematically reduced the piezoelectric response and retention capability, and increased the dielectric constant. All three are detrimental for EH. Undoped compositions should be chosen. We have studied methods to improve the stability of the poled state through aging and self-poling. Introducing the latter into the IDE configuration did not provide sufficiently strong effects to be of practical interest. On the contrary, the aging process may allow to tune the extrinsic contributions to the dielectric and piezoelectric response. It is likely caused by polarization discontinuities at grain boundaries. Further work is needed for fully optimizing this phenomenon. Finally, from the previous investigations, we could deduce and propose golden rules for the design of IDE structures, and discuss typical applications where they are advantageous.