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The protonic ceramic electrochemical cell (PCEC) is an emerging and attractive technology that converts energy between power and hydrogen using solid oxide proton conductors at intermediate temperatures. To achieve efficient electrochemical hydrogen and power production with stable operation, highly robust and durable electrodes are urgently desired to facilitate water oxidation and oxygen reduction reactions, which are the critical steps for both electrolysis and fuel cell operation, especially at reduced temperatures. In this study, a triple conducting oxide of PrNi 0.5 Co 0.5 O 3-δ perovskite is developed as an oxygen electrode, presenting superior electrochemical performance at 400~600 °C. More importantly, the self-sustainable and reversible operation is successfully demonstrated by converting the generated hydrogen in electrolysis mode to electricity without any hydrogen addition. The excellent electrocatalytic activity is attributed to the considerable proton conduction, as confirmed by hydrogen permeation experiment, remarkable hydration behavior and computations. While producing renewable fuel is crucial for a sustainable energy economy, there is still a need for active and durable materials capable of efficient fuel generation and utilization. Here, authors demonstrate a triple-conductive oxide as an oxygen electrode for H 2 or electricity production.

It is of great significance to develop high-temperature anhydrous proton conducting materials. Herein, we report a new strategy to significantly enhance the proton conductivity of covalent organic frameworks (COFs) through expanding the dimensionality of proton conduction. Three COF-based composites, COF-1@PA, COF-2@PA, and COF-3@PA (PA: phosphoric acid), are prepared by PA doping of three COFs with similar pore sizes but different amounts of hydrophilic groups. With the increase of hydrophilic groups, COFs can load more PA because of the enhanced hydrogen–bonding interactions between PA and the frameworks. powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and two-dimensional (2D) solid-state nuclear magnetic resonance (NMR) analyses show that PA can not only enter the channels of COF-3, but also insert into its 2D interlayers. This expands the proton conduction pathways from one-dimensional (1D) to three-dimensional (3D), which greatly improves the proton conductivity of COF-3. Meanwhile, the confinement effect of 1D channels and 2D layers of COF-3 also makes the hydrogen-bonded networks more orderly in COF-3@PA-30 (30 µL of PA loaded on COF-3). At 150 °C, COF-3@PA-30 exhibits an ultrahigh anhydrous proton conductivity of 1.4 S·cm−1, which is a record of anhydrous proton conductivity reported to date. This work develops a new strategy for increasing the proton conductivity of 2D COF materials.

Reducing the operating temperature in the 500–750 °C range is needed for widespread use of solid oxide fuel cells (SOFCs). Proton-conducting oxides are gaining wide interest as electrolyte materials for this aim. We report the fabrication of BaZr 0.8 Y 0.2 O 3− δ (BZY) proton-conducting electrolyte thin films by pulsed laser deposition on different single-crystalline substrates. Highly textured, epitaxially oriented BZY films were obtained on (100)-oriented MgO substrates, showing the largest proton conductivity ever reported for BZY samples, being 0.11 S cm −1 at 500 °C. The excellent crystalline quality of BZY films allowed for the first time the experimental measurement of the large BZY bulk conductivity above 300 °C, expected in the absence of blocking grain boundaries. The measured proton conductivity is also significantly larger than the conductivity values of oxygen-ion conductors in the same temperature range, opening new potential for the development of miniaturized SOFCs for portable power supply. Proton conductor oxides are promising materials for their use as electrolytes for reducing the operation temperature of solid-oxide fuel cells. Epitaxially oriented yttrium-doped barium zirconate films now show unprecedented proton conductivity in the 500–700 °C range.

Two-dimensional covalent organic frameworks (2D COFs) have sparkled wide-ranging research to explore proton-conducting materials. However, the powder-pressed pellets or continuous membranes of 2D COFs are composed of randomly arranged crystallites, which are undesirable for proton transport via a shortcut pathway. We report a controlled strategy for preparing a conformably oriented free-standing COF membrane to address the critical challenge. A monofunctional aldehyde precursor is used as a modulator to enhance reversible association and optimize growth orientation in an interfacial polymerization system. The preferred face-on alignment is achieved throughout the membrane from its flat side to the nanoflake-standing side and, in turn, generates the unidirectional pore channels for accommodating 1,2,4-triazole as proton carriers. The composite merges distinctive features including orientation, crystallinity, porosity, and mechanical strength into one system, exhibiting ultrafast and stable anhydrous proton conduction at high operating temperatures with low activation energy. Our findings offer an innovative strategy for the oriented crystallization of free-standing COF membranes for energy conversion applications.

Sm-doped CeO2-δ (Ce0.9Sm0.1O2-δ; SDC) thin films were prepared on Al2O3 (0001) substrates by radio frequency magnetron sputtering. The prepared thin films were preferentially grown along the [111] direction, with the spacing of the (111) plane (d111) expanded by 2.6% to compensate for a lattice mismatch against the substrate. The wet-annealed SDC thin film, with the reduced d111 value, exhibited surface protonic conduction in the low-temperature region below 100 °C. The O1s photoemission spectrum exhibits H2O and OH− peaks on the SDC surface. These results indicate the presence of physisorbed water layers and the generation of protons on the SDC (111) surface with oxygen vacancies. The protons generated on the SDC surface were conducted through a physisorbed water layer by the Grotthuss mechanism.

Rechargeable aqueous zinc-organic batteries are promising energy storage systems with low-cost aqueous electrolyte and zinc metal anode. The electrochemical properties can be systematically adjusted with molecular design on organic cathode materials. Herein, we use a symmetric small molecule quinone cathode, tetraamino-p-benzoquinone (TABQ), with desirable functional groups to protonate and accomplish dominated proton insertion from weakly acidic zinc electrolyte. The hydrogen bonding network formed with carbonyl and amino groups on the TABQ molecules allows facile proton conduction through the Grotthuss-type mechanism. It guarantees activation energies below 300 meV for charge transfer and proton diffusion. The TABQ cathode delivers a high capacity of 303 mAh g −1 at 0.1 A g −1 in a zinc-organic battery. With the increase of current density to 5 A g −1 , 213 mAh g −1 capacity is still preserved with stable cycling for 1000 times. Our work proposes an effective approach towards high performance organic electrode materials. The flexible structural design of organic materials make them promising candidates for cathode in rechargeable batteries. Here, the authors report a tetraamino-p-benzoquinone cathode which realizes facile proton conduction by the Grotthuss-type mechanism and shows excellent electrochemical performance.

Proton conductive materials are of significant importance and highly desired for clean energy-related applications. Discovery of practical metal-organic frameworks (MOFs) with high proton conduction remains a challenge due to the use of toxic chemicals, inconvenient ligand preparation and complication of production at scale for the state-of-the-art candidates. Herein, we report a zirconium-MOF, MIP-202(Zr), constructed from natural α-amino acid showing a high and steady proton conductivity of 0.011 S cm −1 at 363 K and under 95% relative humidity. This MOF features a cost-effective, green and scalable preparation with a very high space-time yield above 7000 kg m −3 day −1 . It exhibits a good chemical stability under various conditions, including solutions of wide pH range and boiling water. Finally, a comprehensive molecular simulation was carried out to shed light on the proton conduction mechanism. All together these features make MIP-202(Zr) one of the most promising candidates to approach the commercial benchmark Nafion. Metal-organic frameworks are promising materials for proton exchange membrane fuel cells, but cumbersome ligand preparation and use of toxic metals or solvents hinders their application. Here, the authors report the green synthesis of a zirconium, amino acid-based MOF that displays high proton conductivity and excellent stability.

Precise synthesis of polyoxometalates (POMs) is important for the fundamental understanding of the relationship between the structure and function of each building motif. However, it is a great challenge to realize the atomic-level tailoring of specific sites in POMs without altering the major framework. Herein, we report the case of Ce-mediated molecular tailoring on gigantic {Mo 132 }, which has a closed structural motif involving a never seen {Mo 110 } decamer. Such capped wheel {Mo 132 } undergoes a quasi-isomerism with known {Mo 132 } ball displaying different optical behaviors. Experiencing an ‘Inner-On-Outer’ binding process with the substituent of {Mo 2 } reactive sites in {Mo 132 }, the site-specific Ce ions drive the dissociation of {Mo 2 * } clipping sites and finally give rise to a predictable half-closed product {Ce 11 Mo 96 }. By virtue of the tailor-made open cavity, the {Ce 11 Mo 96 } achieves high proton conduction, nearly two orders of magnitude than that of {Mo 132 }. This work offers a significant step toward the controllable assembly of POM clusters through a Ce-mediated molecular tailoring process for desirable properties. Polyoxometalates (POMs) are molecular clusters with diverse structures. Here authors present the synthesis of POMs by Ce-mediated molecular tailoring from gigantic {Mo 132 } into half-closed {Ce 11 Mo 96 }, with proton conductivity nearly two orders of magnitude higher than {Mo 132 }.

The design of stable electrolyte materials with high proton conductivity for use in proton exchange membrane fuel cells remains a challenge. Most of the materials explored have good conductivity at high relative humidity (RH), but significantly decreased conductivity at reduced RH. Here we report a chemically stable and structurally flexible metal–organic framework (MOF), BUT-8(Cr)A, possessing a three-dimensional framework structure with one-dimensional channels, in which high-density sulfonic acid (–SO 3 H) sites arrange on channel surfaces for proton conduction. We propose that its flexible nature, together with its –SO 3 H sites, could allow BUT-8(Cr)A to self-adapt its framework under different humid environments to ensure smooth proton conduction pathways mediated by water molecules. Relative to other MOFs, BUT-8(Cr)A not only has a high proton conductivity of 1.27 × 10 −1  S cm −1 at 100% RH and 80 °C but also maintains moderately high proton conductivity at a wide range of RH and temperature. Proton-conducting metal-organic frameworks (MOFs) could be used as the electrolytes in proton exchange membrane fuel cells but chemically stable materials that perform well at low humidity are still sought. Here the authors prepare a stable, structurally flexible MOF that maintains high proton conductivity under a wide range of humidity.

Water confined within one-dimensional (1D) hydrophobic nanochannels has attracted significant interest due to its unusual structure and dynamic properties. As a representative system, water-filled carbon nanotubes (CNTs) are generally studied, but direct observation of the crystal structure and proton transport is difficult for CNTs due to their poor crystallinity and high electron conduction. Here, we report the direct observation of a unique water-cluster structure and high proton conduction realized in a metal-organic nanotube, [Pt(dach)(bpy)Br] 4 (SO 4 ) 4 ·32H 2 O (dach: (1R, 2R)-(–)-1,2-diaminocyclohexane; bpy: 4,4’-bipyridine). In the crystalline state, a hydrogen-bonded ice nanotube composed of water tetramers and octamers is found within the hydrophobic nanochannel. Single-crystal impedance measurements along the channel direction reveal a high proton conduction of 10 −2 Scm −1 . Moreover, fast proton diffusion and continuous liquid-to-solid transition are confirmed using solid-state 1 H-NMR measurements. Our study provides valuable insight into the structural and dynamical properties of confined water within 1D hydrophobic nanochannels. Water confined in natural or synthetic hydrophobic nano-spaces behaves differently than in the bulk. Here the authors investigate water in hydrophobic synthetic 1D nanochannels revealing water clustering in tetramers and octamers and high proton conductivity, along with a continuous liquid to solid transition.