Plasma-Driven Synthesis of Self-Supported Nickel-Iron Nanostructures for Water Electrolysis

Nickel-based electrocatalysts are deemed as promising low-cost, earth-abundant materials in the development of the next-generation alkaline and anion exchange membrane water electrolyzers. Herein, a plasma-processing technique is presented for fabricating self-supported nanostructures from planar NiFe substrates and its performance for water splitting reactions. Irradiating the samples with helium plasma results in the formation of nano-tendrils, which are affixed to the metallic substrate. This unique design not only enhances charge and mass transport, but also increases the electrochemical surface area by 3 to 4 times, as compared to the unmodified/planar surfaces. For the benchmark 10 mAcm−2geo current density, the nanostructured electrodes demonstrate overpotentials of 330 and 354 mV for oxygen evolution reaction and hydrogen evolution reaction respectively in 1 M KOH. Moving forward, application of this technique can be extended for fabricating self-supported 3D substrates (e.g., foams, felts, perforated sheets), all of which find practical applications in energy conversion and storage devices

An Efficient Strategy for Electroreduction Reactor Outlet Fractioning into Valuable Products

In this work, two industrial dual-step pressure swing adsorption (PSA) processes were designed and simulated to obtain high-purity methane, CO2, and syngas from a gas effluent of a CO2 electroreduction reactor using different design configurations. Among the set of zeolites that was investigated using Monte Carlo and molecular dynamics simulations, NaX and MFI were the ones selected. The dual-PSA process for case study 1 is only capable of achieving a 90.5% methane purity with a 95.2% recovery. As for case study 2, methane is obtained with a 97.5% purity and 95.3% recovery. Both case studies can produce CO2 with high purity and recovery (&gt;97 and 95%, respectively) and syngas with a H2/CO ratio above 4. Although case study 2 allows methane to be used as domestic gas, a much higher value for its energy consumption is observed compared to case study 1 (64.9 vs 29.8 W h molCH4-1).</p

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

Solar hydrogen generation from ambient humidity using functionalized porous photoanodes

Solar hydrogen is a promising sustainable energy vector, and steady progress has been made in the development of photoelectrochemical (PEC) cells. Most research in this field has focused on using acidic or alkaline liquid electrolytes for ionic transfer. However, the performance is limited by (i) scattering of light and blocking of catalytic sites by gas bubbles and (ii) mass transport limitations. An attractive alternative to a liquid water feedstock is to use the water vapor present as humidity in ambient air, which has been demonstrated to mitigate the above problems and can expand the geographical range where these devices can be utilized. Here, we show how the functionalization of porous TiO2 and WO3 photoanodes with solid electrolytes - proton conducting Aquivion and Nafion ionomers - enables the capture of water from ambient air and allows subsequent PEC hydrogen production. The optimization strategy of photoanode functionalization was examined through testing the effect of ionomer loading and the ionomer composition. Optimized functionalized photoanodes operating at 60% relative humidity (RH) and Tcell = 30-70 °C were able to recover up to 90% of the performance obtained at 1.23 V versus reverse hydrogen electrode (RHE) when water is introduced in the liquid phase (i.e., conventional PEC operation). Full performance recovery is achieved at a higher applied potential. In addition, long-term experiments have shown remarkable stability at 60% RH for 64 h of cycling (8 h continuous illumination-8 h dark), demonstrating that the concept can be applicable outdoors

Observation and rationalization of nitrogen oxidation enabled only by coupled plasma and catalyst

Heterogeneous catalysts coupled with non-thermal plasmas (NTP) are known to achieve reaction yields that exceed the contributions of the individual components. Rationalization of the enhancing potential of catalysts, however, remains challenging because the background contributions from NTP or catalysts are often non-negligible. Here, we first demonstrate platinum (Pt)-catalyzed nitrogen (N2) oxidation in a radio frequency plasma afterglow at conditions at which neither catalyst nor plasma alone produces significant concentrations of nitric oxide (NO). We then develop reactor models based on reduced NTP- and surface-microkinetic mechanisms to identify the features of each that lead to the synergy between NTP and Pt. At experimental conditions, NTP and thermal catalytic NO production are suppressed by radical reactions and high N2 dissociation barrier, respectively. Pt catalyzes NTP-generated radicals and vibrationally excited molecules to produce NO. The model construction further illustrates that the optimization of productivity and energy efficiency involves tuning of plasma species, catalysts properties, and the reactor configurations to couple plasma and catalysts. These results provide unambiguous evidence of synergism between plasma and catalyst, the origins of that synergy for N2 oxidation, and a modeling approach to guide material selection and system optimization

Scaling up BiVO₄ Photoanodes on Porous Ti Transport Layers for Solar Hydrogen Production

Commercialization of photoelectrochemical (PEC) water-splitting devices requires the development of large-area, low-cost photoanodes with high efficiency and photostability. Herein, we address these challenges by using scalable fabrication techniques and porous transport layer (PTLs) electrode supports. We demonstrate the deposition of W-doped BiVO4 on Ti PTLs using successive-ionic-layer-adsorption-and-reaction methods followed by boron treatment and chemical bath deposition of NiFeOOH co-catalyst. The use of PTLs that facilitate efficient mass and charge transfer allowed the scaling of the photoanodes (100 cm2) while maintaining ~90 % of the performance obtained with 1 cm2 photoanodes for oxygen evolution reaction, that is, 2.10 mA cm−2 at 1.23 V vs. RHE. This is the highest reported performance to date. Integration with a polycrystalline Si PV cell leads to bias-free water splitting with a stable photocurrent of 208 mA for 6 h and 2.2 % solar-to-hydrogen efficiency. Our findings highlight the importance of photoelectrode design towards scalable PEC device development.</p

Plasma-activated electrolysis for cogeneration of nitric oxide and hydrogen from water and nitrogen

With increasing global interest in renewable energy technology given the backdrop of climate change, storage of electrical energy has become particularly relevant. Most sustainable technologies (e.g., wind and solar) produce electricity intermittently. Thus, converting electrical energy and base molecules (i.e., H2O, N2) into energy-rich ones (e.g., H2, NH3) or chemical feedstock (e.g., NO) is of paramount importance. While H2O splitting is compatible with renewable electricity, N2 fixation is currently dominated by thermally activated processes. In this work, we demonstrate an all-electric route for simultaneous NO and H2 production. In our approach, H2O is reduced to H2 in the cathode of a solid oxide electrolyzer while NO is produced in the anode by the reaction of O2- species (transported via the electrolyte) and plasma-activated N2 species. High faradaic efficiencies up to 93% are achieved for NO production at 650 °C, and NO concentration is >1000 times greater than the equilibrium concentration at the same temperature and pressure

Enhancing the Electrocatalytic Activity of Redox Stable Perovskite Fuel Electrodes in Solid Oxide Cells by Atomic Layer-Deposited Pt Nanoparticles

The carbon dioxide and steam co-electrolysis in solid oxide cells offers an efficient way to store the intermittent renewable electricity in the form of syngas (CO + H2), which constitutes a key intermediate for the chemical industry. The co-electrolysis process, however, is challenging in terms of materials selection. The cell composites, and particularly the fuel electrode, are required to exhibit adequate stability in redox environments and coking that rules out the conventional Ni cermets. La0.75Sr0.25Cr0.5Mn0.5O3 (LSCrM) perovskite oxides represent a promising alternative solution, but with electrocatalytic activity inferior to the conventional Ni-based cermets. Here, we report on how the electrochemical properties of a state-of-the-art LSCrM electrode can be significantly enhanced by introducing uniformly distributed Pt nanoparticles (18 nm) on its surface via the atomic layer deposition (ALD). At 850 °C, Pt nanoparticle deposition resulted in a ∼62% increase of the syngas production rate during electrolysis mode (at 1.5 V), whereas the power output was improved by ∼84% at fuel cell mode. Our results exemplify how the powerful ALD approach can be employed to uniformly disperse small amounts (∼50 μg·cm-2) of highly active metals to boost the limited electrocatalytic properties of redox stable perovskite fuel electrodes with efficient material utilization

Enhancing the Electrocatalytic Activity of Redox Stable Perovskite Fuel Electrodes in Solid Oxide Cells by Atomic Layer-Deposited Pt Nanoparticles

The carbon dioxide and steam co-electrolysis in solid oxide cells offers an efficient way to store the intermittent renewable electricity in the form of syngas (CO + H2), which constitutes a key intermediate for the chemical industry. The co-electrolysis process, however, is challenging in terms of materials selection. The cell composites, and particularly the fuel electrode, are required to exhibit adequate stability in redox environments and coking that rules out the conventional Ni cermets. La0.75Sr0.25Cr0.5Mn0.5O3 (LSCrM) perovskite oxides represent a promising alternative solution, but with electrocatalytic activity inferior to the conventional Ni-based cermets. Here, we report on how the electrochemical properties of a state-of-the-art LSCrM electrode can be significantly enhanced by introducing uniformly distributed Pt nanoparticles (18 nm) on its surface via the atomic layer deposition (ALD). At 850 °C, Pt nanoparticle deposition resulted in a ∼62% increase of the syngas production rate during electrolysis mode (at 1.5 V), whereas the power output was improved by ∼84% at fuel cell mode. Our results exemplify how the powerful ALD approach can be employed to uniformly disperse small amounts (∼50 μg·cm-2) of highly active metals to boost the limited electrocatalytic properties of redox stable perovskite fuel electrodes with efficient material utilization