Protonic Doping Research Articles

Enhancement of Synaptic Performance through Synergistic Indium Tungsten Oxide-Based Electric-Double-Layer and Electrochemical Doping Mechanisms

This study investigated the potential of indium tungsten oxide (IWO) channel-based inorganic electrolyte transistors as synaptic devices. We comparatively analyzed the electrical characteristics of indium gallium zinc oxide (IGZO) and IWO channels using phosphosilicate glass (PSG)-based electrolyte transistors, focusing on the effects of electric-double-layer (EDL) and electrochemical doping. The results showed the superior current retention characteristics of the IWO channel compared to the IGZO channel. To validate these findings, we compared the DC bias characteristics of SiO2-based field-effect transistors (FETs) with IGZO and IWO channels. Furthermore, by examining the transfer curve characteristics under various gate voltage (VG) sweep ranges for PSG transistors based on IGZO and IWO channels, we confirmed the reliability of the proposed mechanisms. Our results demonstrated the superior short-term plasticity of the IWO channel at VG = 1 V due to EDL operation, as confirmed by excitatory post-synaptic current measurements under pre-synaptic conditions. Additionally, we observed superior long-term plasticity at VG ≥ 2 V due to proton doping. Finally, the IWO channel-based FETs achieved a 92% recognition rate in pattern recognition simulations at VG = 4 V. IWO channel-based inorganic electrolyte transistors, therefore, have remarkable applicability in neuromorphic devices.

Proton Conducting Neuromorphic Materials and Devices.

Neuromorphic computing and artificial intelligence hardware generally aims to emulate features found in biological neural circuit components and to enable the development of energy-efficient machines. In the biological brain, ionic currents and temporal concentration gradients control information flow and storage. It is therefore of interest to examine materials and devices for neuromorphic computing wherein ionic and electronic currents can propagate. Protons being mobile under an external electric field offers a compelling avenue for facilitating biological functionalities in artificial synapses and neurons. In this review, we first highlight the interesting biological analog of protons as neurotransmitters in various animals. We then discuss the experimental approaches and mechanisms of proton doping in various classes of inorganic and organic proton-conducting materials for the advancement of neuromorphic architectures. Since hydrogen is among the lightest of elements, characterization in a solid matrix requires advanced techniques. We review powerful synchrotron-based spectroscopic techniques for characterizing hydrogen doping in various materials as well as complementary scattering techniques to detect hydrogen. First-principles calculations are then discussed as they help provide an understanding of proton migration and electronic structure modification. Outstanding scientific challenges to further our understanding of proton doping and its use in emerging neuromorphic electronics are pointed out.

Development of High Performance Thermoelectric Polymers via Doping or Dedoping Engineering.

It is of great significance to develop high-performance thermoelectric (TE) materials, because they can be used to harvest waste heat into electricity and there is abundant waste heat on earth. The conventional TE materials are inorganic semimetals or semiconductors like Bi2Te3 and its derivatives. However, they have problems of high cost, scarce/toxic elements, high thermal conductivity, and poor mechanical flexibility. Organic TE materials emerged as the next-generation TE materials because of their merits including solution processability, low cost, abundant element, low intrinsic thermal conductivity, and high mechanical flexibility. Organic TE materials are mainly conducting polymers because of their high conductivity. Both the conductivity and Seebeck coefficient depend on the doping level, and they are interdependent. Hence, the TE properties of polymers can be improved through doping/dedoping engineering. There are three types of doping forms, oxidative (or reductive) doping, protonic acid doping, and charge transfer doping. Accordingly, they can be dedoped by different approaches. In this article, we review the methods to dope and dedope p-type and n-type TE polymers and the combination of doping and dedoping to optimize their TE properties. Secondary doping is also covered, since it can significantly enhance the conductivity of some TE polymers.

Enhanced Photocatalytic CO2 Reduction by Amine Functionalization of Graphitic Carbon Nitride

Graphitic carbon nitride (g‐CN) is a promising photocatalyst for solar fuel generation, but its charge carrier mobility, charge recombination, and CO2 reduction/H2 evolution efficacy and selectivity are a strong function of the synthesis and postsynthesis techniques employed. Protonation and phosphorous doping of g‐CN yield promise visible light activities, promoting enhanced CO2 reduction and hydrogen evolution. However, the amine‐functionalized surface chemistry of g‐CN gains little attention in open literature. Herein, g‐CN and phosphorus‐doped g‐CN are synthesized via facile one‐pot pyrolysis and subjected to protonation postsynthesis to quantify the influence of common strategies on surface amine content and photocatalyst activity for H2 evolution and CO2 reduction. Material characterization confirms the exfoliation of the photocatalyst and change in the amine functionalization of the surface. The amorphous phosphorus‐doped g‐CN material exhibits a high number of surface amine groups, increasing the adsorption prior to reduction and enhancing selectivity for CO2 reduction.

Proton doping enhanced flexoelectricity and photocurrent in hydrogen-charged TiO2

The intrinsic flexoelectric effect observed in oxide materials often falls below the desired threshold for practical applications. In this work, we demonstrate proton doping in insulating rutile TiO2 crystal as an effective approach to significantly increase flexoelectricity by more than two orders of magnitude. We attribute the noteworthy enhancement of flexoelectricity to the dual impact of proton doping in oxide materials. First, proton doping serves to induce the presence of charge carriers, resulting in the generation of flexoelectric currents. Second, proton doping induces expansion and distortion of the lattice structure, leading to an amplified flexoelectric field when the crystal experiences a strain gradient. The formation of O–H bonding in TiO2 crystal provides another route to break centrosymmetry according to lattice distortion of the TiO2 lattice, resulting in a larger flexoelectric field. In addition, the introduction of proton doping in TiO2 single crystals leads to a substantial increase in photocurrent by effectively flattening the interfacial Schottky junction. This phenomenon results in a three-order of magnitude enhancement of the photocurrent. Our work broadens the horizon of study on dielectric materials through proton doping and may also provide an approach that enables the utilization of dielectric materials in energy conversion applications.

Doped HfOxNanoclusters: Polar and Resistive Switching in the Smallest Functional Units

In the study presented in this article, the impact of proton doping on the structural and electronic properties of hafnium oxide nanoclusters is investigated, with a focus on their potential for use in resistive and polar switching devices. In the results, it is shown that the incorporation of protons can stabilize the cage‐like crystalline structures of clusters, leading to reversible changes in electronic properties by varying oxygen stoichiometry. However, the full coverage of hafnia atoms by hydrogen removes in‐gap states, highlighting the importance of controlled moisture content in redox‐based memristive devices and neuromorphic units. In addition, in this study, the polar properties of these clusters are explored, illustrating possible polar switching in metastable pure , low‐barrier antiferroelectric‐like switching in carbon‐stabilized , and low‐barrier polar switching in . In these findings, the potential of clusters is revealed as active components for next‐generation high‐capacity nonvolatile electronic memory and beyond von Neumann computing in sub‐nanometer scale.

Synergistically boosted photocatalytic production of hydrogen peroxide via protonation and oxygen doping on graphitic carbon nitride

Photocatalytic synthesis of hydrogen peroxide (H2O2) using modified graphitic carbon nitride (g-C3N4) has been recognized as a promising green and sustainable process. However, the effect of g-C3N4 modification on the surface properties of photocatalytic surface reactions still needs extended exploration. In this work, we design and synthesize a protonation induced oxygen doping in g-C3N4 (pCN1), which shows uniquely curled nanosheet structures in microscopic level. Under visible light irradiation, the photocatalytic H2O2 production rate of pCN1 reaches 707 μmol g−1 h−1, which is approximately eight times higher than that of primitive g-C3N4. The enhanced photocatalytic performance is attributed to the synergistic effect of protonation and oxygen doping, which not only dramatically facilitates the adsorption of oxygen molecules and the desorption of H2O2 product, but also promotes the charge separation. In addition, more abundant protons supplied via protonation process can combine with the adjacent oxygen atoms on catalyst surface, thus promoting the formation of OOH* intermediate and improving the H2O2 yield. This work provides a facile and effective strategy to prepare highly-efficient modified g-C3N4 photocatalyst for the clean and convenient synthesis of H2O2.

Proton is Essential or Not: A Fresh Look on Pseudocapacitive Energy Storage of PANI Composites.

Protonation has been considered essential for the pseudocapacitive energy storage of polyaniline (PANI) for years, as proton doping in PANI chains not only activates electron transport pathways, but also promotes the proceeding of redox reactions. Rarely has the ability for PANI of storing energy without protonation been investigated, and it remains uncertain whether PANI has pseudocapacitive charge storage properties in an alkaline electrolyte. Here, this work first demonstrates the pseudocapacitive energy storage for PANI without protonation using a PANI/graphene composite as a model material in an alkaline electrolyte. Using in situ Raman spectroscopy coupled with electrochemical quartz crystal microbalance (EQCM) measurements, this work determines the formation of -N= group over potential on a PANI chain and demonstrates the direct contribution of OH- in the nonprotonation type of oxidation reactions. This work finds that the PANI/graphene composite in an alkaline electrolyte has excellent cycling stability with a wider operation voltage of 1V as well as a slightly higher specific capacitance than that in an acidic electrolyte. The findings provide a new perspective on pseudocapacitive energy storage of PANI-based composites, which will influence the selection of electrolytes for PANI materials and expand their application in energy storage fields.

X-ray magnetic circular dichroism and anomalous Hall effect in proton-doped spinel NiCo2O4 thin films

Element-specified x-ray magnetic circular dichroism (XMCD) and the anomalous Hall effect (AHE) have been investigated to provide deep insights into the magnetic and electronic structural evolutions of different proton-doping spinel ${\mathrm{NiCo}}_{2}{\mathrm{O}}_{4}$ (NCO) films. Our results show that the magnetic dichroism at the Co ${L}_{23}$-edge is mainly contributed by the spin magnetic moment at the tetrahedral (${T}_{d}$)-site ${\mathrm{Co}}^{2+}$ in pristine NCO. The spin magnetic moments at Co and Ni sites have antiparallel alignments. The magnetic anisotropy is related to the considerable orbital magnetic moments therein. Upon proton-doping in ${\mathrm{NCO}}_{\text{int}}$ films (the intermediate state with the mixed phases of ${\mathrm{H}}_{x}\mathrm{NCO}$ and NCO), the magnetic dichroism at the Co ${L}_{23}$-edge still exists. The doping of one extra electron resides at the octahedral (${O}_{h}$)-site ${\mathrm{Co}}^{3+}$ partially and changes ${\mathrm{Co}}^{3+}$ ($S=0)$ to ${\mathrm{Co}}^{2+}$ ($S=3/2$). This ${O}_{h}$-site ${\mathrm{Co}}^{2+}$ aligns in an antiparallel manner with ${T}_{d}$-site ${\mathrm{Co}}^{2+}$ through O-ions mediated antiferromagnetic superexchange interaction, resulting in a reduced spin magnetic moment in ${\mathrm{NCO}}_{\text{int}}$ compared to pristine NCO films. Moreover, the reduced magnetic anisotropy in ${\mathrm{NCO}}_{\text{int}}$ is due to the decreasing of the orbital magnetic moment, which can be related to the charge redistribution at Co $3d$ energy levels and the crystal-field effect. In the two-proton doped ${\mathrm{H}}_{2}\mathrm{NCO}$ films, the magnetic dichroism is absent where the antiferromagnetism arises from the antiparallel spin alignments of ${\mathrm{Co}}^{2+}$ in ${T}_{d}$ and ${O}_{h}$ sites. The intrinsic ferromagnetism is also verified by the AHE, which shows a square-shaped hysteresis as a function of the magnetic fields for pristine NCO and ${\mathrm{NCO}}_{\text{int}}$. Interestingly, the proton-doped ${\mathrm{NCO}}_{\text{int}}$ films exhibit an enhanced coercive field and the exchange bias effect with an asymmetric hysteresis loop at low temperatures, which can be ascribed to the antiferromagnetic phase stemming from partial Co valence state reduction by proton doping.

Phonons Damped by Proton Doping in Barium Zirconate

Phonons Damped by Proton Doping in Barium Zirconate

Manipulate the magnetic and electronic states in NiCo2O4 films through protonation

Element doping and substitution have been widely used for the engineering of the electronic structure and macroscopic magnetic properties of various materials. However, traditional doping process does not allow further optimization after preparation of the samples. Hydrogen annealing-induced protonation has emerged as a powerful method for the efficient control of uniaxial lattice expansion to modulate the physics properties of the otherwise inaccessible novel correlated phases in oxide thin-films. Here, we report the modulation of the magnetic moment, magneto-transport and electrical-transport in inverse-spinel NiCo2O4 (NCO) by protonation. Strong dependence of saturation magnetic moment and electrical conduction on deposition temperature and proton doping parameters has been systematically investigated. The magnetoresistance ratio of the protonated NCO could be increased by 400% by engineering of the doping condition and thus the phase configuration. These findings indicate that protonation is one effective strategy for regulation and optimization of NCO-based magnetic and electric devices.

High-Performance Phototransistor Memory with an Ultrahigh Memory Ratio Conferred Using Hydrogen-Bonded Supramolecular Electrets

As the research of photonic electronics thrives, the enhanced efficacy from an optic unit cell can considerably improve the performance of an optoelectronic device. In this regard, organic phototransistor memory with a fast programming/readout and a distinguished memory ratio produces an advantageous outlook to fulfill the demand for advanced applications. In this study, a hydrogen-bonded supramolecular electret is introduced into the phototransistor memory, which comprises porphyrin dyes, meso-tetra(4-aminophenyl)porphine, meso-tetra(p-hydroxyphenyl)porphine, and meso-tetra(4-carboxyphenyl)porphine (TCPP), and insulated polymers, poly(4-vinylpyridine) and poly(4-vinylphenol) (PVPh). To combine the optical absorption of porphyrin dyes, dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) is selected as a semiconducting channel. The porphyrin dyes serve as the ambipolar trapping moiety, while the insulated polymers form a barrier to stabilize the trapped charges by forming hydrogen-bonded supramolecules. We find that the hole-trapping capability of the device is determined by the electrostatic potential distribution in the supramolecules, whereas the electron-trapping capability and the surface proton doping originated from hydrogen bonding and interfacial interactions. Among them, PVPh:TCPP with an optimal hydrogen bonding pattern in the supramolecular electret produces the highest memory ratio of 1.12 × 108 over 104 s, which is the highest performance among the reported achievements. Our results suggest that the hydrogen-bonded supramolecular electret can enhance the memory performance by fine-tuning their bond strength and cast light on a potential pathway to future photonic electronics.

Alan Graham MacDiarmid. 14 April 1927—7 February 2007

Alan G. M ac Diarmid was an inorganic chemist by training who pioneered the field of synthetic metals. He grew up in a family that lived frugally, and he had to work in the Chemistry Department of the Victoria University of Wellington as a laboratory assistant before he could undertake part-time degree studies. He was awarded a Fulbright Scholarship to the University of Wisconsin, where he completed his first PhD with Norris Hall. The desire to receive a higher degree in the UK led to a Shell Scholarship to complete a second doctorate with Harry Emeléus FRS. After a sojourn at the University of St Andrews, Alan M ac Diarmid was appointed to an academic position at the University of Pennsylvania, where he remained essentially for his whole career. His early research was based on the properties of silicon hydrides, but he also became interested in poly(sulfur nitride). This led to a search in collaboration with Alan J. Heeger for intrinsically conducting non-metallic materials. A chance meeting with Hideki Shirakawa at the University of Tokyo led to M ac Diarmid being shown thin metallic-like films of poly(acetylene) made in Shirakawa's laboratory. Shirakawa travelled to Philadelphia to collaborate with M ac Diarmid and Heeger on the halogen ‘doping’ of poly(acetylene), which led to the discovery that the doped material was an excellent conductor. Thus, the field of synthetic metals was born. This paradigm-shifting work in which a polymer was shown to be a conductor led to the award of the 2000 Nobel Prize in Chemistry to these three individuals. M ac Diarmid went on to study in great detail the properties of polyaniline; the fact that it could be processed from solution and further modified by oxidative and protonic doping led to all sorts of potentially interesting opportunities in optoelectronics. From all this research, the modern field of organic electronic materials emerged as an important disruptive technology whose advancement depended on an entirely new branch of interdisciplinary science.

Proton-Induced Defect-Rich Vanadium Oxides as Reversible Polysulfide Conversion Sites for High-Performance Lithium Sulfur Batteries.

Lithium-sulfur (Li-S) batteries have attracted attention due to their high theoretical energy density, natural abundance, and low cost. However, the diffusion of polysulfides decreases the utilization and further degrades the battery's life. We have successfully fabricated a defect-rich layered sodium vanadium oxide with proton doping (HNVO) nanobelt and used it as the functional interface layer on the separator in Li-S batteries. Benefiting from the abundant defects of NVO and the catalytic activity of metal vanadium in the electrochemical process, the shuttle of polysulfides was greatly decreased by reversible chemical adsorption. Moreover, the extra graphene layer contributes to accelerating the charge carrier at high current densities. Therefore, a Li-S battery with G@HNVO delivers a high capacity of 1494.8 mAh g-1 at 0.2 C and a superior cycling stability over 700 cycles at 1 C. This work provides an effective strategy for designing the electrode/separator interface layer to achieve high-performance Li-S batteries.

Manipulated magnetic coercivity and spin reorientation transition in NiCo2O4 films

Half-metallic NiCo2O4 with high spin polarizability has great potential applications in spintronics. The manipulation of magnetic anisotropy is crucial for spintronics based on spin-transfer or spin–orbit torques, as it is directly related to the critical switching current density. Here, we report epitaxial growth of metallic NiCo2O4 film with perpendicular magnetic anisotropy on MgAl2O4 single crystal substrates. The modulation of the magnetic anisotropy was achieved by changing the growth conditions (deposition temperature and thickness) of NiCo2O4 films and by means of protonation. Strong dependence of magnetic coercivity on deposition temperature (350–500 °C) has been observed due to variable phase configuration. Furthermore, the magnetic coercive field can also be effectively controlled by the film thickness (3–78 nm) through strain relaxation. More importantly, spin reorientation transition has been achieved by proton and electron doping in the NiCo2O4 films, resulting in reconfigured valence states of Ni and Co cations and a magnetic easy axis rotation from out-of-plane to in-plane. The effective modulation of the magnetic anisotropy provides important insights into the functional design of NiCo2O4-based spintronics with ultralow energy dissipation.

Solid-state survey of boronate-substituted polyaniline: on the mechanism of conductivity, electroactivity, and interactions with polyols

We provide a comprehensive investigation of chemical states in boronate-substituted polyaniline (PANI) in a wide range of pH and potentials. According to X-ray photoelectron spectroscopy data, the boronate substituent allows to sustain up to 10–15% of protonated amino groups in neutral and basic media, while for unsubstituted PANI this form disappears at pH above 7.4. According to electrochemical measurements, such additional proton doping results in a substantial prolongation of the polymer electroactivity and conductivity to basic pH. It retains resistivity of the polymer film below 1000 Ω m up to pH 9, gaining over two orders of magnitude in conductivity compared with the unsubstituted PANI. In contrast to generally accepted paradigm that the negatively charged –B(OH)3− group existing in neutral solutions promotes PANI doping, XPS and MAS 11B NMR spectroscopy data indicate that charged tetrahedral form appears only in strongly alkaline solutions at pH above 11. In the frame of suggested mechanism, the boronic acid substituent with trigonal coordination acts as a local dissociation center, providing constant protonation of the imine/amine bridges. The mechanism involves water or protonated ligand (saccharide or hydroxy acid) coordination by –B(OH)2 and the boronate group deprotonation followed by H+ transfer to the bridging imine/amine, which triggers redox response of the backbone conductive chain. A comprehensive solid-state survey gives a deeper insight into the interaction of substituted PANIs with non-electroactive species and opens new prospects for introducing rich boronate chemistry to sensing and electrocatalysis.

Amphiphilic Peptoid-Directed Assembly of Oligoanilines into Highly Crystalline Conducting Nanotubes.

It is reported herein the synthesis of a novel amphiphilic diblock peptoid bearing a terminal conjugated oligoaniline and its self-assembly into small-diameter (D ≈ 35nm) crystalline nanotubes with high aspect ratios (>30). It is shown that both tetraaniline (TANI)-peptoid and bianiline (BANI)-peptoid triblock molecules self-assemble in solution to form rugged highly crystalline nanotubes that are very stable to protonic acid doping and de-doping processes. The similarity of the crystalline tubular structure of the nanotube assemblies revealed by electron microscopy imaging, and X-ray diffraction analysis of the nanotube assemblies of TANI-functionalized peptoids and nonfunctionalized peptoids showed that the peptoid is an efficient ordered structure directing motif for conjugated oligomers. Films of doped TANI-peptoid nanotubes has a dc conductivity of ca. 95 mScm-1 , while the thin films of doped un-assembled TANI-peptoids show a factor of 5.6 lower conductivity, demonstrating impact of the favorable crystalline ordering of the assemblies on electrical transport. These results demonstrate that peptoid-directed supramolecular assembly of tethered π-conjugated oligo(aniline) exemplify a novel general strategy for creating rugged ordered and complex nanostructures that have useful electronic and optoelectronic properties.

Exciton Delocalization in a DNA-Templated Organic Semiconductor Dimer Assembly.

A chiral dimer of an organic semiconductor was assembled from octaniline (octamer of polyaniline) conjugated to DNA. Facile reconfiguration between the monomer and dimer of octaniline–DNA was achieved. The geometry of the dimer and the exciton coupling between octaniline molecules in the assembly was studied both experimentally and theoretically. The octaniline dimer was readily switched between different electronic states by protonic doping and exhibited a Davydov splitting comparable to those previously reported for DNA–dye systems employing dyes with strong transition dipoles. This approach provides a possible platform for studying the fundamental properties of organic semiconductors with DNA-templated assemblies, which serve as candidates for artificial light-harvesting systems and excitonic devices.

Synergistically Boosted Photocatalytic Production of Hydrogen Peroxide Via Protonation and Oxygen Doping on Graphitic Carbon Nitride

Synergistically Boosted Photocatalytic Production of Hydrogen Peroxide Via Protonation and Oxygen Doping on Graphitic Carbon Nitride

Resistance-switchable conjugated polyrotaxane for flexible high-performance RRAMs.

A representative closely packed conjugated polyrotaxane (CPR1) is synthesized by threading polyaniline (PAN) into β-cyclodextrin (CD) macrocycles and utilized for the first time to construct an RRAM device that exhibits an outstanding resistive switching capability. The CPR1 RRAM device displays remarkable nonvolatile memory performance with an extremely high ON/OFF ratio of 108, the ultra-fast response of 29 ns, excellent reliability and reproducibility, and long-term stability (more than 1 year). The mechanism underlying this resistive switching behavior is understood according to the electric-field-induced proton doping of the PAN core by the CD sheath through hydrogen bonding interactions. More impressively, the favorable solubility and intrinsic flexibility of CPR1 allow for large-scale fabrication of flexible CPR1 RRAM device arrays by full-printing technology with endurance of 1000 bending cycles at the minimum bending radius of 3 mm, higher ON/OFF ratio of 108, and relatively lower operating voltage of 1.8 V. This work shows the potential of CPR materials in highly stable memory devices for next-generation flexible and wearable electronics.