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Moisture-electric generators (MEGs), harvesting ubiquitous moisture from the environment for electricity generation, have attracted great interest as power supply devices. However, there are great challenges associated with material availability, fabrication accessibility and operation environment, which are key factors to achieve high output with low cost for practical applications, and a deeper understanding of the underlying mechanism of interactions between MEGs and water is urgently required. Here, a whey protein available in supermarkets is used to fabricate low-cost MEGs with controllable performance through tuning surface charges and hydrophilicity, which provides new insights into the electricity generation mechanism and large-scale application. The MEGs exhibit the highest voltage output of 1.45 V at a room humidity level of 40% relative humidity. The whey protein films possess the merits of low cost (70 times cheaper than commonly used polymers), being flexible and semi-transparent, and having self-healing ability, presenting excellent comprehensive device performance. Besides, MEGs can operate well at extreme temperatures (-20 degrees C or 50 degrees C) and power a location tracker in a desert with 26% relative humidity. The modified functional layers with selective ion absorption and controllable outputs provided a deeper understanding of electricity generation in MEGs and demonstrated great potential in powering a wide range of electronic devices in various dynamic environments with high sustainability and reliability. Refereed/Peer-reviewed

A high-throughput screening of piezo-photocatalytic materials based on first-principles calculations and a simple electrostatic model is presented that identifies new bulk compounds able to catalyse the water splitting reaction under sunlight.

The new class of oxide heterojunctions with mixed dimensionalities holds great promise for energy and environmental applications. However, the existing fabrication strategies typically involve low-yield and multistep processes leading to the formation of powders that necessitate binding agents when used for electrochemical applications; thereby, the durability and performance of the resultant electrode may be adversely impacted. To address these challenges, the present work first reports a high-temperature counter-current gas flow technique for rapid fabrication (5–10 min) of centimetre-size, self-adhesive, free-standing 3D patches made of ZnO-based woven nanowires. Furthermore, the high applicability of the method was shown by layer-by-layer assembly of the ZnO and layers of 0D heteroatoms including Bi2O3, CdO, SnO2, and carbon forming stratified oxide heterojunction (SOH) nanostructures with midgap states within their electronic bandgap region. This work is innovative in that the ZnO and the fabricated SOHs are synthesised through a sustainable and large-scale method based on microrecycling of waste materials. The engineering of the electronic band positions can modify the functionality of the SOH patches by optimising the potentials required for catalytic reactions. As a representative, the SOH nanostructures were tested for anodic electrocatalytic water oxidation to H2O2. The results showed that the ZnO–CdO patch has the lowest overpotential of 150 mV and outstanding stability at 2.33 V vs. RHE. Furthermore, the results of first-principles density functional theory (DFT) calculations (i) confirmed realignments of the band position due to the formation of midgap states, and (ii) revealed that significant improvements in the electrocatalytic H2O2 performance can be achieved with overpotentials as low as 0.19 and 0.31 V for ZnO–CdO and ZnO–Bi2O3, respectively. This work offers an ultrafast fabrication strategy to synthesise binder-free SOH nanostructures with an engineered electronic structure that can be an alternative to state-of-the-art noble metal electrocatalysts such as Pt.

In this work, a new surface engineering technique through UV/ozone treatment to improve the oxygen evolution reaction performance of nickel-iron hydroxide based catalysts has been developed. It is found that UV/ozone treatment can significantly improve the hydrophilicity of the catalysts as well as modify the electronic structure at the Ni–Fe center and oxidize Ni2+ to Ni3+, which consequently enables better electrode–electrolyte contacts, stronger charge-transfer and more numbers of active sites with higher intrinsic activity during the OER. This work demonstrates UV/ozone treatment as a highly effective strategy towards the rational design of high-performance electrocatalysts by exploiting surface modifications.

Polymer Electrolyte Membrane Fuel Cells (PEMFC) are often viewed as enablers of decarbonised energy systems since they transform hydrogen directly into electricity with water as the main by-product. The attraction for fuel cells is also in their versatility because they can be implemented across a wide range of applications from microelectronics to large scale power generation. Herein, we review recent progress on the design and fabrication of PEMFC with a special focus on their air-breathing planar configuration as this extends the possibility of PEMFC to thin and flexible designs. To date, the deployment of planar PEMFC highly depends upon scientific progress and technological solutions for cost reduction and long-term durability including the development of better proton conducting membranes and platinum-free catalysts to drive the oxygen reduction and hydrogen oxidation reactions efficiently. Long term durability is another challenge that can be addressed through the advancement of inexpensive and lightweight current collectors and highly efficient gas diffusion electrodes for better distribution of the reactants while maintaining an optimum hydration of the proton conducting membrane. Innovative fabrication methods for the various components of planar PEMFC as well as effective stack design and assembly are also critical for efficiency maximization, reproducibility and overall cost reduction.

The present work reports a detailed mechanistic interpretation of the role of the solubility of dopants and resultant midgap defect energies in band gap engineering. While there is a general perception that a single dopant is associated with single solubility and defect mechanisms, in reality, the potential for multiple solubility and defect mechanisms requires a more nuanced interpretation. Similarly, Kroger–Vink defect equilibria assume that stoichiometries during substitutional and interstitial solid solubility as well as Schottky and Frenkel pair formation are compensated by the diffusion of matrix ions to the grain boundaries or surface. However, this approach does not allow the possibility that stoichiometry is uncompensated, where diffusion of the matrix ion to lattice interstices occurs, followed by charge compensation by redox of this ion. Consequently, a modified defect equilibria formalism has been developed in order to allow description of this situation. Experimental data for the structural, chemical, semiconducting, and photocatalytic properties as a function of doping level are correlated with conceptual structural models, a comprehensive energy band diagram, and the corresponding defect equilibria. These correlations reveal the complex mechanisms of the interrelated solubility and defect formation mechanisms, which change significantly and irregularly as a function of small changes in doping level. The analyses confirm that the assumption of single mechanisms of solid solubility and defect formation may be simplifications of more complex processes. The generation of (1) a matrix of complementary characterisation and analytical data, (2) the calculation of a complete energy band diagram, (3) consideration of charge compensation mechanisms and redox beyond the limitations of Kroger–Vink approaches, and (4) the development of models of corresponding structural analogies combine to create a new approach to interpret and explain experimental data. These strategies allow deconstruction of these complex issues and thus targeting of optimal and possibly unique doping levels to achieve lattice configurations that may be energetically and structurally unfavorable. These approaches then can be applied to other doped semiconducting systems.

Thermoelectric materials create an electric potential when subjected to a temperature gradient and vice versa; hence they can be used to harvest waste heat into electricity and in thermal management applications. However, finding highly efficient thermoelectrics with high figures of merit, zT ≥ 1, is very challenging because the combination of a high power factor and low thermal conductivity is rare in materials. Here, we use first-principles methods to analyze the thermoelectric properties of Li2SnX3 (X = S, and Se), a recently synthesized class of lithium fast-ion conductors presenting high thermal stability. In p-type Li2SnX3, we estimate highly flat electronic valence bands that produce high Seebeck coefficients exceeding 400 μV K−1 at 700 K. In n-type Li2SnX3, the electronic conduction bands are slightly dispersive; however, the accompanying electron–acoustic phonon scattering is weak, which induces high electrical conductivity. The combination of a high Seebeck coefficient and electrical conductivity gives rise to high power factors, reaching a maximum of ∼4.5 mW m−1 K−2 at 300 K in both n-type Li2SnS3 and Li2SnSe3. Likewise, the thermal conductivity in Li2SnX3 is low as compared to conventional thermoelectric materials, 1.35–4.65 W m−1 K−1 at room temperature. As a result, we estimate a maximum zT of 1.1 in n-type Li2SnS3 at 700 K and of 2.1 (1.1) in n-type Li2SnSe3 at the same temperature (300 K). Our findings of large zT in Li2SnX3 suggest that lithium fast-ion conductors, typically employed as electrolytes in solid-state batteries, hold exceptional promise as thermoelectric materials.

Compositional engineering of BiFeO3 can significantly boost its photovoltaic performance. Therefore, controlling site substitution and understanding how it affects the optical and electronic properties while achieving robust and stable phases is essential to continue progressing in this field. Here the influence of cation co-substitution in BiFeO3 on phase purity, optical and electronic properties is investigated by means of X-ray diffraction, spectroscopic ellipsometry and X-ray absorption spectroscopy, respectively. Piezoelectric force microscopy and ferroelectric characterization at room temperature has been carried out in co-doped BiFeO3 films. First-principles calculations are also performed and compared to the experimental observations. It is shown that the incorporation of La3+ in Bi(Fe,Co)O3 films improves phase purity and stability while preserving the reduced band gap achieved in metastable Bi(Fe,Co)O3. Moreover, it is suggested that the changes in the optoelectronic properties are mainly dictated by the hybridisation between unoccupied Co 3d and O 2p states along with the presence of Co3+/Co2+ species. This thorough study on (Bi,La)(Fe,Co)O3 thin films coupled with the use of a cost-effective and facile solution deposition synthesis increases the motivation to continue exploiting the potential of these perovskite materials., This research was supported by the Spanish Ministerio de Ciencia, Innovación y Universidades (“Severo Ochoa” Programme for Centres of Excellence in R&D CEX2019-000917-S, MAT2017-83169-R, RTI2018-093996-B-C32, PID2019-107727RB-I00 (AEI/FEDER, EU)). P. M. thanks financial support from FPI fellowship (PRE2018-084618). C. M. and C. C. acknowledge computational resources and technical assistance from the Australian Government and the Government of Western Australia through the National Computational Infrastructure (NCI) and Magnus under the National Computational Merit Allocation Scheme and The Pawsey Supercomputing Centre. The authors acknowledge Prof. J. Fontcuberta for providing access to his experimental facilities and the support of ALBA staff for the successful performance of the measurements at CIRCE beamline of the ALBA Synchrotron Light Source. I. F. and C. C. acknowledge support from the Spanish Ministry of Science, Innovation and Universities under the “Ramón y Cajal” fellowship RYC2017-226531 and RYC2018-024947-I, respectively. M. C and I. F acknowledge Beca Leonardo from fundación BBVA. H. T is financially supported by China Scholarship Council (CSC) with no. 201906050014. The work of P. M. and H. T have been done in the framework of the doctorate in Materials Science of the Autonomous University of Barcelona.

The first photoswitchable bimetallic gold catalysts based on an azobenzene backbone have been synthesized and their catalytic properties have been investigated. In the intramolecular hydroamination reaction, the reaction rate proved to be dependent on the E- or Z-configuration of the catalyst used, with the Z-isomer being significantly more active. These results suggest that a possible cooperative effect between the two metals operates in this reaction.

We predict a covalent functionalization strategy for precise immobilization of peptides on carbon nanostructures immersed in water, based on atomistic first-principles simulations. The proposed strategy consists of straightforward decoration of the carbon nanosurfaces (CNS, e.g. graphene and nanotubes) with calcium atoms. This approach presents a series of improvements with respect to customary covalent CNS functionalization techniques: (i) intense and highly selective biomolecule–CNS interactions are accomplished while preserving atomic CNS periodicity, (ii) under ambient conditions calcium-decorated CNS and their interactions with biomolecules remain strongly attractive both in vacuum and aqueous environment, and (iii) calcium coatings already deplete the intrinsic hydrophobicity of CNS thus additional functionalization for CNS water miscibility is not required. The observed biomolecule–CNS binding enhancement can be explained in terms of large electronic transfers from calcium to the oxygen atoms in the carboxyl and side-chain groups of the peptide. The kind of electronic, structural and thermodynamic properties revealed in this work strongly suggest the potential of Ca-decorated CNS for applications in drug delivery and biomaterials engineering.