One step electrochemical fabrication of high performance Ni@Fe-doped Ni(oxy)hydroxide anode for practical alkaline water electrolysis

Oxygen evolution reaction (OER) is a rate-determining process in alkaline water electrolysis (AWE). Herein, we report a novel one-step oxidation-electrodeposition (OSOE) approach to generate core@shell nanoarrays-based AWE electrode with outstanding OER performances: an overpotential of 245 mV at 10 mA cm−2 (Tafel slope: 37 mV dec−1), and excellent stability under huge current densities. Moreover, the alkaline (AEL) cell equipped with NM-OSOE-23 anode recorded significant performance improvement of 200 mV lower voltage (2 A cm−1) compared with a similar cell used bare Ni mesh as an anode, which was contributed by notable enhancements of interface contact, anodic charge transfer, and mass transfer. These promising results are attributed to the constructed specific core@shell Ni@Fe-doped Ni(oxy)hydroxide nanoarray architecture on commercial nickel mesh. This study demonstrates this first reported OSOE can be commercialized to make highly efficient anodes enabling next-generation AWE

Mixed hydride-electronic conductivity in Rb2CaH4 and Cs2CaH4

Hydride-ion conductors and mixed hydride-electronic conductors are promising materials for various applications, especially in (electro)chemical energy conversion and storage. Many of the hydride-ion conductors discovered to date are oxyhydrides with the K2NiF4-type structure. In this work, Cs2CaH4 and Rb2CaH4, which crystallize in the K2NiF4-type structure, were synthesized and electrochemically characterized. By employing electrochemical impedance spectroscopy (EIS) and single-step chronoamperometry measurements, it is found that both materials show mixed ionic-electronic conductivity at moderate (100–200 °C) temperatures. The overall conductivity of both materials is increased by the release of hydrogen at elevated temperatures, indicating an effect of hydride vacancy concentration on the conductivity. This suggests that the ionic conductivity is due to hydride-ion transport, which is further supported by Climbing Imaged Nudged Elastic Band (CINEB) calculations. Cs2CaH4 shows approximately equal ionic and electronic conductivity at 190 °C (total conductivity σ = 2.1 × 10−6 S cm−1), while Rb2CaH4 (σ = 8.8 × 10−7 S cm−1 at 190 °C) is primarily an ionic conductor. As mixed hydride-electronic conductors, both materials show promise in chemical conversion and energy conversion applications

CO2 conversion via coupled plasma-electrolysis process

Surplus renewable electricity used to convert CO2 into CO, the building block of liquid fuels, advances the energy transition by enabling large-scale, long-term energy storage and the synthesis of fuel for long-haul transportation. Among the various technologies developed, renewable electricity driven conversion of CO2 by high-temperature electrolysis and by plasmolysis offer a tantalising potential. High-temperature electrolysis is characterized by high-yield and energy-efficiency and the direct separation of the CO2 dissociation products CO and O2. However, the difficulty to break the carbon-oxygen double bond poses challenging requirements on electrode materials. CO2 plasmolysis on the other hand, offers a similar energy efficiency, does not employ scarce materials, is easy to upscale, but requires efficient gas separation and recuperation because the produced CO remains mixed with O2 and residual CO2. Here, we demonstrate that the coupling of the two processes leads to a renewable-electricity-driven route for producing CO from CO2, overcoming the main bottleneck of CO2 plasmolysis. A simulated CO2 plasmolysis gas mixture is supplied to a high-temperature electrolyser to separate the product gases electrochemically. Our results show that the product stream of the coupled-process contains 91% less oxygen and 138% more CO compared with the bare plasmolysis process. Apart from upgrading the produced gas mixture, this coupled approach benefits from material stability. Durability tests (~100 h) show better stability in coupled operation when compared with conventional CO2 electrolysis. Synergy between plasmolysis and electrolysis opens up a novel route to efficient CO2 conversion into valuable CO feedstock for the synthesis of long-chain hydrocarbons

Roadmap on exsolution for energy applications

Over the last decade, exsolution has emerged as a powerful new method for decorating oxide supports with uniformly dispersed nanoparticles for energy and catalytic applications. Due to their exceptional anchorage, resilience to various degradation mechanisms, as well as numerous ways in which they can be produced, transformed and applied, exsolved nanoparticles have set new standards for nanoparticles in terms of activity, durability and functionality. In conjunction with multifunctional supports such as perovskite oxides, exsolution becomes a powerful platform for the design of advanced energy materials. In the following sections, we review the current status of the exsolution approach, seeking to facilitate transfer of ideas between different fields of application. We also explore future directions of research, particularly noting the multi-scale development required to take the concept forward, from fundamentals through operando studies to pilot scale demonstrations

Use of solid state ionic conductors for the study of methane reforming and/or coupling in the presence of steam

In the present thesis double-chamber solid state proton and oxygen ion conducting cells were used for the simultaneous production of C2 hydrocarbons and hydrogen or electricity from methane in the presence of steam. Various catalytic systems were tested for the simultaneous production of C2’s and hydrogen or C2’s and electricity in the proton conducting cell. The most important were a mixture of Au and Ce-Na2WO4/SiO2 (Au-CNWS), the perovskite La0,6Sr0,4Co0,8Fe0,2O3-a (LSCF) and Ag. The catalytic experiments with Ag showed good catalytic activity for the production of ethane, ethylene and hydrogen with C2 selectivities above 50 % in many cases. In the proton pumping experiments the production rates of the useful products increased and the separation of hydrogen was again high (80-90 %). In the cogeneration experiments (fuel cell) the greatest power production (of the systems tested) was achieved at 3.89 mW with a concurrent C2 yield enhancement of 25 %. In the present thesis the possibility of simultaneous production of ethane, ethylene and hydrogen in an oxygen ion conducting cell, Ag/YSZ/Pt is also presented. In this setup the cathode (Pt) is fed with steam instead of oxygen or air. On the application of a constant current steam is electrolyzed (H2O + 2 e- H2 + O2-) and the oxygen ions are transported through the electrolyte lattice to the anode (Ag) where they react with methane to form C2’s (CH4 + O2- C2H6 + C2H4 + H2O + 2e-). Hydrogen is thus produced in a chamber separate from the C2’s making separation much easier. It was found that controlling the electrochemical supply of oxygen could tune the system to either higher hydrogen or higher C2 yields. The maximum yield in ethane and ethylene combined was 5.65 % with a hydrogen production rate of 1.4∙10-6 mol/s (70 % of the steam feed) at 840 oC, but at least 50 % of the oxygen did not react on the Ag electrode and desorbed to the gas phase. In order to take advantage of the desorbing oxygen, a quantity of catalyst for the oxidative coupling of methane (OCM) was added to the Ag/YSZ/Pt cell (on the Ag electrode) leading to a new type of hybrid solid electrolyte/fixed bed cell. In this way the C2 yield was enhanced from 4.8 to 8.1 % when using Ce-Na2WO4/SiO2 at 800 oC and from 0.6 to 7.4 % when using SrZr0.95Y0.05O3-a at 720 oC compared to plain Ag (under the same conditions). Finally, the stability of the hybrid cells was verified for 12 to 16 hour runs, under constant current. Future studies should focus on a very few materials (one or two membrane types and catalysts) with the construction of a reactor similar to a commercial one, and on long term stability tests. A further investigation of the MnxCe1-x-Na2WO4/SiO2 catalyst family would be a good starting point.Στη παρούσα διατριβή χρησιμοποιήθηκαν αντιδραστήρες κυψέλης στερεών αγωγών πρωτονίων και ιόντων οξυγόνου με σκοπό την ταυτόχρονη παραγωγή και διαχωρισμό C2 υδρογονανθράκων (αιθυλένιο, αιθάνιο) και υδρογόνου ή ηλεκτρικής ενέργειας από το μεθάνιο παρουσία υδρατμών. Στον αντιδραστήρα κυψέλης του πρωτονιακού αγωγού δοκιμάστηκαν διάφορα καταλυτικά συστήματα για την ταυτόχρονη παραγωγή C2’s και υδρογόνου ή C2’s και ηλεκτρικής ενέργειας από το μεθάνιο. Τα πιο σημαντικά ήταν Au και Ce-Na2WO4/SiO2 (Au-CNWS), περοβσκίτης La0,6Sr0,4Co0,8Fe0,2O3-a (LSCF) και Ag. Τα καταλυτικά πειράματα παρουσία Ag έδειξαν καταλυτική ενεργότητα για την παραγωγή αιθυλενίου, αιθανίου και υδρογόνου από το μεθάνιο με εκλεκτικότητες προς αιθυλένιο και αιθάνιο συνολικά που ξεπέρασαν σε πολλές περιπτώσεις το 50 %. Στα πειράματα άντλησης πρωτονίων οι ρυθμοί σχηματισμού των ωφέλιμων προϊόντων της διεργασίας αυξήθηκαν με τον διαχωρισμό του υδρογόνου να είναι και εδώ σε υψηλά επίπεδα (80-90 %). Στη μελέτη χημικής συμπαραγωγής (κυψέλη καυσίμου) επιτεύχθηκε η μέγιστη παραγόμενη ισχύς από όσα συστήματα εξετάστηκαν (3.89 mW) με την απόδοση προς C2’s να παρουσιάζει βελτίωση έως και 25 % στο σημείο της μέγιστης ισχύος. Στη παρούσα διατριβή παρουσιάζεται επίσης η πιθανότητα της ταυτόχρονης παραγωγής αιθανίου, αιθυλενίου και υδρογόνου χρησιμοποιώντας κυψέλη ηλεκτρολύτη ανιόντων οξυγόνου, Ag/YSZ/Pt. Στη παρούσα διάταξη δεν ήταν απαραίτητη η τροφοδοσία αέριου οξυγόνου, αλλά υδρατμών στον θάλαμο της Pt (κάθοδος). Με την εφαρμογή σταθερού ρεύματος οι υδρατμοί ηλεκτρολύονται (H2O + 2 e- H2 + O2-) και τα ιόντα οξυγόνου μεταφέρονται μέσα από το πλέγμα του ηλεκτρολύτη στην άνοδο (Ag) όπου και αντιδρούν με το μεθάνιο για τον σχηματισμό C2’s (CH4 + O2- C2H6 + C2H4 + H2O + 2e-). Το υδρογόνο έτσι, ελευθερώνεται ως αέριο σε ξεχωριστό θάλαμο από αυτόν που γίνεται ο σχηματισμός των C2’s κάνοντας τον διαχωρισμό του πολύ ευκολότερο. Επιπλέον, βρέθηκε ότι η πιθανότητα ρύθμιση της ηλεκτροχημικής τροφοδοσίας δίνει την δυνατότητα ρύθμισης του ρυθμού παραγωγής των C2’s και του υδρογόνου σε διαφορετικές συνθήκες. Η μέγιστη απόδοση σε αιθυλένιο και αιθάνιο συνολικά ήταν 5.65 % με έναν σύγχρονο ρυθμό παραγωγής υδρογόνου 1.4.10-6 mol/s (70 % των υδρατμών) στους 840 oC, αλλά περισσότερο από το 50 % του οξυγόνου δεν αντέδρασε στην επιφάνεια του Ag και ελευθερωνόταν στην αέρια φάση. Για να είναι δυνατή η εκμετάλλευση του αέριου οξυγόνου φορτώθηκε στην ηλεκτροκαταλυτική κυψέλη Ag/YSZ/Pt ποσότητα καταλύτη οξειδωτικού διμερισμού στην επιφάνεια του Ag δημιουργώντας μία νέου τύπου υβριδική κυψέλη στερεού ηλεκτρολύτη και καταλυτικής κλίνης. Με αυτόν τον τρόπο η απόδοση προς C2’s βελτιώθηκε από 4.8 σε 8.1 % στους 800 oC χρησιμοποιώντας τον Ce-Na2WO4/SiO2 και από 0.6 σε 7.4 % στους 720 oC με χρήση του SrZr0.95Y0.05O3-a από τις αντίστοιχες που λήφθηκαν με καθαρό Ag. Τέλος, έγινε έλεγχος σταθερότητας των υβριδικών κυψελών οι οποίες κρίθηκαν σταθερές για 12-16 h εφαρμογής σταθερού ρεύματος. Μία μελλοντική έρευνα στη παρούσα διεργασία πρέπει να βασιστεί στην επιλογή ελάχιστων υλικών, δηλαδή ένα με δύο τύπους μεμβρανών και καταλυτών. Μία περαιτέρω διερεύνηση στους καταλύτες της οικογένειας MnxCe1-x-Na2WO4/SiO2 θα μπορούσε να είναι το πρώτο βήμα

Improvement of stress multi-tolerance and bioethanol production by Saccharomyces cerevisiae immobilised on biochar: Monitoring transcription from defence-related genes

The study determined the protective role of using biochar as immobilisation carrier against multiple stresses encountered by Saccharomyces cerevisiae assessing transcription from important metabolic routes involved in the molecular mechanisms triggered during inhibitory bioprocess conditions. Immobilised cells exhibited higher bioethanol titre (39 g L−1) and productivity (7.72 g L−1 h−1) at elevated temperatures compared with the suspended culture that yielded 34 g L−1 and 1.99 g L−1 h−1 respectively. Fermentation at 39 °C resulted in 2.15-fold increase of HSP104 relative mRNA expression in suspended cells, while the gene was induced by 0.5-fold using the immobilised biocatalyst. A similar response occurred for HSF1 and TPS exhibiting 3.0- and 3.8-fold increase using suspended cells as opposed to the application of immobilised cells where transcription of the aforementioned genes was raised by 0.0- and 2.6-fold upon temperature increase respectively. Transcription from MSN2/MSN4 under the aforementioned conditions indicated the protective role of cell attachment on the biomaterial against stimulation of the heat shock response route and oxidative stress. Although fermentations conducted under ethanol stress resulted in failure of the conventional process, immobilised cells produced 21 g L−1 bioethanol exhibiting 7 g L−1 h−1 productivity, while monitoring transcription of HSP12 and HSP104 demonstrated the beneficial use of the proposed technology. Proline accumulation during osmotic stress further supported the elevated bioethanol productivity achieved by the immobilised system, which was 74% higher as opposed to the conventional process. The study confirmed that S. cerevisiae immobilisation on biochar conferred cells with heat tolerance, ethanol tolerance, osmotolerance and improved fermentation capacity. The technology proposed constitutes a sustainable technological alternative to strain modification improving multiple stress-tolerance in bioethanol fermentations

Deep reconstruction of Ni-Al-based pre-catalysts for a highly efficient and durable anion-exchange membrane (AEM) electrolyzer

The anion exchange membrane (AEM) electrolyzer has shown great potential for producing green hydrogen. However, this technology is still in its early stages and has not yet been applied on an industrial scale. One of the most significant challenges is the lack of cost-effective and scalable techniques for producing highly active, durable, and earth-abundant metal-based catalysts. Herein, we present a scalable thermal spraying process for fabricating defect-rich nickel-based HNA-CA that can function as an efficient pre-catalyst for both (hydrogen evolution reaction) HER and (oxygen evolution reaction) OER. Particularly, after deep reconstruction through simple electrochemical activation, the obtained HNA-CA-H and HNA-CA-O exhibit the lowest overpotential of −31 mV (HER) and 188 mV (OER) at 10 mA cm−2, surpassing that of noble metal-based catalysts such as Pt and IrO2, respectively. By coupling two 5 cm2 electrodes, the resulting HNA-CA-H(-)‖HNA-CA-O(+) AEM electrolyzer cell demonstrates exceptional performance, achieving an extraordinarily low cell voltage of 1.89 V at 1 A cm−2 (1 M KOH, room temperature). Furthermore, it showcases remarkable durability, sustaining operation for an impressive 500 hours at 5 A (1 A cm−2). These performance metrics notably outclass the majority of AEM electrolyzers reported under comparable operational settings. The outcomes can primarily be ascribed to the substantial improvements in interfacial contact, charge transfer efficiency, and mass transport mechanisms, all of which were comprehensively unveiled through in situ impedance analysis, ex situ structural characterization, and a thorough investigation of wettability and bubble dynamics. These findings hold significant promise for expediting the advancement and practical deployment of AEM electrolysis technology.</p