Internal Proton Research Articles

Water Status Detection Method Based on Water Balance Model for High-Power Fuel Cell Systems

With the gradually accelerating pace of global decarbonization, highly efficient and clean proton exchange membrane fuel cells (PEMFCs) are considered to be an energy solution for the future. During the operation of a fuel cell, it is necessary to keep the internal proton exchange membrane in a good state of hydration, so an appropriate method of detecting the hydration state is essential. At present, fuel cell systems are rapidly developing towards high power, but methods for detecting the hydration state of high-power fuel cell systems are still relatively lacking. Therefore, this paper studies the hydration state of high-power fuel cell systems and builds a condensation tail-gas water collection device for calculating the water flow out of a fuel cell system, deriving the hydration status inside the high-power fuel cell system. To verify the proposed water balance model, a series of experiments were conducted based on controlled variables such as working temperature, air metering ratio, and load current. Experiments were conducted on a 100 KW fuel cell system to collect water flow from the fuel cell system. Finally, based on the experimental data, the change rate of the internal water content of the fuel cell system under different conditions was calculated. The results show that, under the same load current, as the working temperature and air metering ratio increase, the change rate of the internal water content of the fuel cell system gradually decreases. Therefore, at low power, it is necessary to maintain an appropriate working temperature, while at high power, maintaining an appropriate air metering ratio is more important.

Influence of compression effect on the MEA structure and performance based on M−N–C electrocatalysts for PEMFC

The single-atom dispersed active sites and the thicker catalytic layer of metal-nitrogen-carbon (M-N-C) electrocatalysts based membrane electrode assembly (MEA) exhibit notable distinctions from Pt-based MEA, necessitating targeted optimization. This study systematically investigates the influence of compression on both structure and performance of the M-N-C electrocatalysts based MEA. Four compression ratios, ranging from 11.5% to 39.3%, were examined across diverse operational conditions. The variations in impedance across different electrochemical regions are observed, resulting from the superposition of distinct impedance components. It is found that the insufficient compression leads to higher porosity and the formation of cracks between catalytic layer and membrane, adversely impacting internal resistance and proton transport. Increasing compression first acts the catalytic layer, and then gradually acts on the interface, membrane and gas diffusion layer, thereby reducing internal resistance, charge transfer resistances, albeit at the expense of heightened mass transfer resistance. Among these factors, the influence of internal resistance affects significance to total performance. Furthermore, compression influenced mass transfer differently in various layers. For the catalyst layer, the effect was uniform and sustained, while for the gas diffusion layer, it initially remained constant and then experienced a sudden deterioration over a certain extent. Optimal MEA performance is achieved when the compression ratio attains 40 %, which 2.1 times higher than the low compression MEA. This finding emphasizes the necessity for higher compression on M-N-C electrocatalysts based MEA compared to Pt-based MEA.

Electrochemistry of Diquinonyl Amines with an Internal Proton Source

It is well established that quinones play an important role in various biological systems. Studying electrochemical properties of quinones affords fundamental knowledge of semi-quinone radicals formation in vivo and in vitro in different media.Following our previous work on electrochemical properties of various quinonyl amines [1], Scheme 1 below describes seven diquinonyl amines. Noteworthy that six of them (1-6) contain an internal proton donor (‘NH’) except for the seventh one (7), in which both quinone moieties are attached to ‘NMe’ group. Their redox potentials were measured by cyclic voltammetry in dichloromethane [2].The results show a strong dependence of the nature of substituent on the first reduction potentials, and that protonation of diquinonyl amines is feasible by internal proton source even in a non-polar medium.

Proton transfer in cytochrome bd-I from E. coli involves Asp-105 in CydB

Cytochrome bds are bacterial terminal oxidases expressed under low oxygen conditions, and they are important for the survival of many pathogens and hence potential drug targets. The largest subunit CydA contains the three redox-active cofactors heme b558, heme b595 and the active site heme d. One suggested proton transfer pathway is found at the interface between the CydA and the other major subunit CydB. Here we have studied the O2 reduction mechanism in E. coli cyt. bd-I using the flow-flash technique and focused on the mechanism, kinetics and pathway for proton transfer.Our results show that the peroxy (P) to ferryl (F) transition, coupled to the oxidation of the low-spin heme b558 is pH dependent, with a maximum rate constant (~104 s−1) that is slowed down at higher pH. We assign this behavior to rate-limitation by internal proton transfer from a titratable residue with pKa ~ 9.7. Proton uptake from solution occurs with the same P➔F rate constant. Site-directed mutagenesis shows significant effects on catalytic turnover in the CydB variants Asp58B➔Asn and Asp105B➔Asn variants consistent with them playing a role in proton transfer. Furthermore, in the Asp105B➔Asn variant, the reactions up to P formation occur essentially as in the wildtype bd-I, but the P➔F transition is specifically inhibited, supporting a direct and specific role for Asp105B in the functional proton transfer pathway in bd-I. We further discuss the possible identity of the high pKa proton donor, and the conservation pattern of the Asp-105B in the cyt. bd superfamily.

Redox-active “Structural Pillar” molecular doping strategy towards High-Performance polyaniline-based flexible supercapacitors

To coordinate flexibility to electrodes without sacrificing their electrochemical properties is critical for the development of wearable supercapacitors (SCs). Polyaniline (PANI) is well-known pseudocapacitive electrode material due to its high conductivity and different oxidation states upon switchable structures. However, its rigid conjugated backbone and structural instability caused by repeated doping/de-doping during cycling severely impede its utilization in flexible SCs. Herein, we deploy a directional freezing and redox-active “structural pillar” molecular doping strategy to boost PANI-based flexible SCs with high performance. The directional freezing strategy constructs an interconnected 3D honeycomb hydrogel structure with PANI nanofibers, which guarantees fast ion diffusion and electron transport and meanwhile exposes abundant active sites. The large-sized dopant 2-amino-4-bromoanthraquinone-2-sulfonic acid sodium (AQNS) is used as the structural pillar to alleviate the structural instability of PANI during cycling and provides additional pseudocapacitance arising from its redox active quinone groups. Moreover, the negatively charged −SO3− on AQNS can further interact with H+ in the electrolyte to act as an internal proton reservoir, assisting the protonation of –NH- and −N = in PANI to facilitate its charge storage process. Consequently, the PANI-AQNS electrode achieves a high specific capacitance of 578 F g−1 at 1 A g−1 and its symmetric SCs exhibit a specific capacitance of 199 F g−1 at 0.5 A g−1 with an energy density of 13.61 W h kg−1 at a power density of 175 W kg−1. Upon 2000 cycles of dynamic deformations, the SCs can still maintain above 90 % of the initial capacitance, verifying their excellent flexibility-relevant property.

Promoting Water Oxidation by Proton Acceptable Groups Surrounding Catalyst on Electrode Surface.

Large-scale hydrogen production through water splitting represents an optimal approach for storing sustainable but intermittent energy sources. However, water oxidation, a complex and sluggish reaction, poses a significant bottleneck for water splitting efficiency. The impact of outer chemical environments on the reaction kinetics of water oxidation catalytic centers remains unexplored. Herein, chemical environment impacts were integrated by featuring methylpyridinium cation group (Py+) around the classic Ru(bpy)(tpy) (bpy = 2,2'-bipyridine, tpy = 2,2':6',2''-terpyridine) water oxidation catalyst on the electrode surface via electrochemical co-polymerization. The presence of Py+ groups could significantly enhance the turnover frequencies of Ru(bpy)(tpy), surpassing the performance of typical proton acceptors such as pyridine and benzoic acid anchored around the catalyst. Mechanistic investigations reveal that the flexible internal proton acceptor anions induced by Py+ around Ru(bpy)(tpy) are more effective than conventionally anchored proton acceptors, which promoted the rate-determining proton transfer process and enhanced the rate of water nucleophilic attack during O-O bond formation. This study may provide a novel perspective on achieving efficient water oxidation systems by integrating cations into the outer chemical environments of catalytic centers.

Techno-economic assessment of hydrogen as a fuel for internal combustion engines and proton exchange membrane fuel cells on long haul applications

Powertrain energy conversion and management are critical factors in providing affordable and robust solutions for transport decarbonization. Various powertrain technologies are being proposed to reduce the impacts of transportation-related carbon dioxide emissions, such as battery electric, fuel cell, and conventional vehicles running with lower carbon fuels. Specifically for the commercial sector, hydrogen internal combustion engines and fuel cells are being extensively discussed. In this sense, this investigation evaluates the benefits and areas of enhancement for hydrogen internal combustion engines and fuel cells from a techno-economic perspective. Power plant models were developed and validated in GT-Power, and detailed investigations on the energy loss pathways were performed. In addition, the powertrains are included in full longitudinal vehicle models and submitted to different driving cycles, representing homologation and real-world driving conditions, with the intent to understand the effect of the cycles from a global energy management perspective. Finally, the fuel consumption results are used as inputs for a total cost of ownership calculation to determine the economic viability of each powertrain. Overall, fuel cells offered efficient operation across the conditions assessed, with engine-powered powertrains showing reduced efficiencies ranging from 23 % to 63 % depending on the cycle and payload. The limited peak efficiency for the spark-ignited low-pressure hydrogen direct injection engine was a dominant factor for the reduced performance of this platform. Strategies for efficiency improvement are identified that could lead to improved internal combustion engine operation. Despite the limited efficiency benefits of hydrogen internal combustion engines, total cost of ownership calculations show hydrogen internal combustion engines being the most cost-effective solution in the near to medium-term scenario.

Evidence for transporter-mediated uptake of environmental L-glutamate in a freshwater sponge, Ephydatia muelleri.

The freshwater sponge, Ephydatia muelleri, lacks a nervous or endocrine system and yet it exhibits a coordinated whole-body action known as a "sneeze" that can be triggered by exposure to L-glutamate. It is not known how L-glutamate is obtained by E. muelleri in sufficient quantities (i.e., 70µM) to mediate this response endogenously. The present study tested the hypothesis that L-glutamate can be directly acquired from the environment across the body surface of E. muelleri. We demonstrate carrier mediated uptake of two distinct saturable systems with maximal transport rates (Jmax) of 64.27 ± 4.98 and 25.12 ± 1.87 pmols mg-1min-1, respectively. The latter system has a higher calculated substrate affinity (Km) of 2.87 ± 0.38µM compared to the former (8.75 ± 1.00µM), indicative of distinct systems that can acquire L-glutamate at variable environmental concentrations. Further characterization revealed potential shared pathways of L-glutamate uptake with other negatively charged amino acids, namely D-glutamate and L-aspartate, as well as the neutral amino acid L-alanine. We demonstrate that L-glutamate uptake does not appear to rely on exogenous sodium or proton concentrations as removal of these ions from the bathing media did not significantly alter uptake. Likewise, L-glutamate uptake does not seem to rely on internal proton motive forces driven by VHA as application of 100nM of the VHA inhibitor bafilomycin did not alter uptake rates within E. muelleri tissues. Whether the acquired amino acid is used to supplement feeding or is stored and accumulated to mediate the sneeze response remains to be determined.

Comparative performance analysis of different hydrogen power composite cycles with waste heat recovery

ABSTRACT Hydrogen energy has been under close scrutiny by countries around the world. At present, the main technologies for utilizing hydrogen energy in transport power systems are hydrogen internal combustion engine (HICE) and proton exchange membrane fuel cell (PEMFC). Since both of them generate a large amount of waste heat, and waste heat recovery technology is one of the most promising means of utilizing waste heat to improve efficiency, this paper makes a comprehensive comparison of the two technologies in composite waste heat recovery (WHR) system in terms of modeled maximum efficiency, full operating condition efficiency and future predicted maximum efficiency. Based on the thermal efficiency analysis, the advantages, disadvantages, and development prospects of the two technologies in composite the WHR system are reevaluated. The results demonstrate that the efficiency of the HICE and PEMFC can be improved by 6.83% and 2.81%, with the use of WHR system, respectively. Under the full range of operating conditions, the HICE-WHR composite system has obvious efficiency advantage in middle-high load working condition, but PEMFC-WHR composite system has obvious efficiency advantage in low load working condition. Both of them will be very competitive and potential technology routes of hydrogen energy utilization for land transportation.

Theoretical study of direct internal protonation of a [1.1.1]cryptand by proton carriers

The use of a strongly basic proton carrier (e.g. ammonia) inhibits the external protonation of [1.1.1]cryptand amines and allows rapid internal protonation without the use of strong acids.

Theoretical study of electrochemical reduction of CO2 to CO using a nickel-N4-Schiff base complex.

The electrochemical reduction (ECR) of CO2 to CO by nickel-N4-Schiff base complexes as catalysts was investigated using density functional theory (DFT). Three nickel complexes, 1-Ni, 2-Ni, and [2-Ni]Me were considered. Two CO2 reduction pathways, i.e., external and internal proton transfer, were proposed and their reaction energy profiles were computed. The external proton transfer pathway which includes three steps has no transition state. The reaction energies for all steps are exothermic and the reaction catalyzed by 1-Ni has the lowest overall reaction energy (-5.72 eV) followed by those by 2-Ni (-5.56 eV) and [2-Ni]Me (-5.54 eV). The internal proton transfer pathway is composed of four steps. The internal proton transfer step (carboxylic formation) includes a transition state. The CO2 reduction by [2-Ni]Me could not proceed via this mechanism, since [2-Ni]Me does not have an NH group in the ligand and 1-Ni has a lower activation energy (0.83 eV), which is in agreement with the experiment. The charge of the pre-adsorption nickel complex seems to be related to the activity of the catalysts. The catalyst with a less positive nickel charge is more active.

Selective recognition of Zn(II) by a novel Schiff base chemosensor with the formation of an AIE active Zn(II) complex having picric acid detection ability: Application in live cell imaging study

The present work highlights the development and spectroscopic identification of a Schiff base chemosensor, (Z)-4-bromo-2-(((1-methoxybutan-2-yl)imino)methyl)phenol, (HL), for selective detection Zn(II) via turn-on fluorescence among a number of competing cations in a 9:1 DMSO-water media. The high binding constant value, measured during titration of HL and Zn(II), boosts to conduct a straightforward condensation reaction between HL and Zn(II) which results in solid crystals of Zn(II) complex (complex 1). In 7:3 DMSO-water media, complex 1 display Aggregation Induced Emission (AIE) behavior, as a result of which, with increasing the water percentage, under UV light optically the cyan color complex 1 solution converts to green color with the enhancement of fluorescence intensity. The UV, fluorescence, DLS, and SEM studies, fully approve the probe's AIE active behavior. The AIE active property of complex 1 is implemented to detect picric via turn-off fluorescence. The chelation-induced enhanced fluorescence (CHEF) on and Excited state internal proton transfer (ESIPT) off are the key factors in showing the luminescence property of complex 1 and the distortion of aggregation behavior of complex 1 in the presence of picric acid leads to the turn-off fluorescence of the complex 1 solution. The mass spectral and IR spectral analysis supports the 1:1 stoichiometric addition of the probe and analyte and the structure of the probe-analyte complexes is optimized using density Functional Theory (DFT) study. Finally, the live cell imaging study enables us to independently verify the biosensing behavior of complex 1 and HL towards Zn(II) and picric acid respectively.

Internal Proton Transfer in the Activation of Heliorhodopsin

Heliorhodopsin (HeR), a recently discovered new rhodopsin family, contains a single counterion of the protonated Schiff base, E108 in HeR from Thermoplasmatales archaeon SG8-52-1 (TaHeR). Upon light absorption, the M and O intermediates form in HeRs, as well as type-1 microbial rhodopsins, indicating that the proton transfer from the Schiff base leads to the activation of HeRs. The present flash photolysis study of TaHeR in the presence of a pH-sensitive dye showed that TaHeR contains a proton-accepting group (PAG) inside protein. Comprehensive mutation study of TaHeR found the E108D mutant abolishing the M formation, which is not only at pH 8, but also at pH 9 and 10. The lack of M observation does not originate from the short lifetime of the M intermediate in E108D, as FTIR spectroscopy revealed that a red-shifted K-like intermediate is long lived in E108D. It is likely that the K-like intermediate returns to the unphotolyzed state without internal proton transfer in E108D. E108 and D108 are the Schiff base counterions of the wild-type and E108D mutant TaHeR, respectively, whereas small difference in length of side chains determine internal proton transfer reaction from the Schiff base. Based on the present finding, we propose that the internal water cluster (four water molecules) constitutes PAG in the M intermediate of TaHeR. In the wild type TaHeR, a protonated water cluster is stabilized by forming a salt bridge with E108. In contrast, slightly shortened counterion (D108) cannot stabilize the protonated water cluster in E108D, and thus impairs internal proton transfer from the Schiff base.

Long-life P-type co-doped polyaniline cathodes for ultrahigh-energy-density aqueous zinc-ion batteries

Conductive polyaniline (PANI) is considered as a promising cathode material for aqueous zinc-ion batteries (AZIBs) due to its reversible redox properties. In this study, we prepared a binder-free PANI (βPG-PANI-6) cathode co-doped with β-naphthalene sulfonic acid (β-NSA), HClO4, and graphitic acid (GA) via a layer-by-layer self-assembled electro-polymerization method. As a soft template, β-NSA micelles can be doped with HClO4 into PANI nanoparticles to prevent the tight accumulation of PANI chains. Moreover, β-NSA and GA adsorbed on the surface of PANI nanoparticles through layer-by-layer self-assembly contain abundant weak acid groups, which can act as internal proton reservoirs to offer protons to guarantee high redox activity. During the electro-polymerization process, the flexible GA matrix which forms NO bond closely with PANI can alleviate the volume expansion effect of PANI. As a result, the βPG-PANI-6 cathode can obtain superior discharge specific capacity (560.5 mAh/g, 0.2 A/g), excellent rate performance (251.3 mAh/g, 10 A/g). It is commendable that the AZIBs assembled by βPG-PANI-6 cathode deliver ultra-high energy density and power density (535.31 Wh/kg @ 187.16 W/kg, 184.45 Wh/kg @ 7378.01 W/kg). This study expands the doping chemistry of PANI and advances the development of conducting polymer for AZIBs to a new level.

Engineering sulfuric acid-pretreated biochar supporting MnO2 for efficient toxic organic pollutants removal from aqueous solution in a wide pH range

Manganese dioxides (MnO2) and biochar materials are both desirable candidates for environmental remediation of toxic organic pollutants (TOPs) in water due to wide availability and environmental-friendly. In practical application, however, MnO2 suffers from low redox activity owing to deprotonation, while biochar is subject to limited removal capacity. Herein, a difunctional engineering sulfuric acid-pretreated biochar supporting MnO2 composite (MBC-A) was firstly synthesized and optimized to remove various TOPs from aqueous solution. Specifically, sulfuric acid not only served as an active agent to improve the specific surface area of biochar for improvement of adsorption capacity and more MnO2 loading, but also facilitated the introduction of sulfonic acid groups (-SO3H) as an internal proton reservoir to inhibit inactivation of MnO2 due to deprotonation in alkaline. Thanks to adsorption and oxidation, MBC-A showed excellent removal capacity (214.9 mg/g) and fast reaction kinetics (360 min) for tetracycline (TC), exceeding precursor and other materials reported in literature. Importantly, the effective operation pH range of MBC-A was broadened to 1–13 with the help of buffering capacity of –SO3H groups. The dominant driving force of adsorption were π-π interaction and hydrogen bond; while reactive oxidative species were mainly ascribed to singlet oxygen (1O2), hydroxyl radical (·OH) and reactive Mn3+. The possible reactive sites and pathway were investigated by combining experimental results with density functional theory (DFT) calculation. Further, the results of multiple cyclic runs, removal in real river water and toxicity assessment demonstrated well reusability, high environmental security, and excellent practical applicability of MBC-A.

Physicochemical homeostasis in bacteria.

In living cells the biochemical processes such as energy provision, molecule synthesis, gene expression and cell division take place in a confined space where the internal chemical and physical conditions are different from those in dilute solutions. The concentrations of specific molecules and the specific reactions and interactions vary for different types of cells, but a number of factors are universal and kept within limits, which we refer to as physicochemical homeostasis. For instance, the internal pH of many cell types is kept within the range of 7.0 to 7.5, the fraction of macromolecules occupies 15-20% of the cell volume (also know as macromolecular crowding) and the ionic strength is kept within limits to prevent salting-in or salting-out effects. In this article we summarize the generic physicochemical properties of the cytoplasm of bacteria, how they are connected to the energy status of the cell, and how they affect biological processes (Figure 1). We describe how the internal pH and proton motive force are regulated, how the internal ionic strength is kept within limits, what the impact of macromolecular crowding is on the function of enzymes and the interaction between molecules, how cells regulate their volume (and turgor), and how the cytoplasm is structured. Physicochemical homeostasis is best understood in Escherichia coli, but pioneering studies have also been performed in lactic acid bacteria.

Charging Current and Proton Flux Measurements From Medium Earth Orbit and the Slot Region

We present data from the sister instruments Merlin and CREDANCE (Cosmic Radiation Environment Dosimetry and Charging Experiment), from medium Earth orbit (MEO) and the slot region respectively. Each instrument measures internal charging current, proton and ion flux, and total ionizing dose with an identical suite of instruments. In this paper we present charging current and proton flux data. Merlin flew on board the Giove-A MEO testbed spacecraft from December 2005 to November 2021. CREDANCE flew on board the Demonstration and Science Experiments (DSX) spacecraft from July 2019 to May 2021.

Low-Voltage Driven Ionic Polymer-Metal Composite Actuators: Structures, Materials, and Applications.

With the characteristics of low driving voltage, light weight, and flexibility, ionic polymer-metal composites (IPMCs) have attracted much attention as excellent candidates for artificial muscle materials in the fields of biomedical devices, flexible robots, and microelectromechanical systems. Under small voltage excitation, ions inside the IPMC proton exchange membrane migrate directionally, leading to differences in the expansion rate of the cathode and the anode, which in turn deform. This behavior is caused by the synergistic action of a three-layer structure consisting of an external electrode layer and an internal proton exchange membrane, but the electrode layer is more dominant in this process due to the migration and storage of ions. The exploration of modifications and alternatives for proton exchange membranes and recent advances in the fabrication and characterization of conductive materials, especially carbon-based materials and conductive polymers, have contributed significantly to the development of IPMCs. This paper reviews the progress in the application of proton exchange membranes and electrode materials for IPMCs, discusses various processes currently applied to IPMCs preparation, and introduces various promising applications of cutting-edge IPMCs with high performance to provide new ideas and approaches for the research of new generation of low-voltage ionic soft actuators.

Dynamics and Proton Conduction of Heterogeneously Confined Imidazole in Porous Coordination Polymers

AbstractThe nanoconfinement of proton carrier molecules may contribute to the lowing of their proton dissociation energy. However, the free proton transportation does not occur as easily as in liquid due to the restricted molecular motion from surface attraction. To resolve the puzzle, herein, imidazole is confined in the channels of porous coordination polymers with tunable geometries, and their electric/structural relaxations are quantified. Imidazole confined in a square‐shape channels exhibits dynamics heterogeneity of core‐shell‐cylinder model. The core and shell layer possess faster and slower structural dynamics, respectively, when compared to the bulk imidazole. The dimensions and geometry of the nanochannels play an important role in both the shielding of the blocking effect from attractive surfaces and the frustration filling of the internal proton carrier molecules, ultimately contributing to the fast dynamics and enhanced proton conductivity.

Dynamics and Proton Conduction of Heterogeneously Confined Imidazole in Porous Coordination Polymers.

The nanoconfinement of proton carrier molecules may contribute to the lowing of their proton dissociation energy. However, the free proton transportation does not occur as easily as in liquid due to the restricted molecular motion from surface attraction. To resolve the puzzle, herein, imidazole is confined in the channels of porous coordination polymers with tunable geometries, and their electric/structural relaxations are quantified. Imidazole confined in a square-shape channels exhibits dynamics heterogeneity of core-shell-cylinder model. The core and shell layer possess faster and slower structural dynamics, respectively, when compared to the bulk imidazole. The dimensions and geometry of the nanochannels play an important role in both the shielding of the blocking effect from attractive surfaces and the frustration filling of the internal proton carrier molecules, ultimately contributing to the fast dynamics and enhanced proton conductivity.