Hydrogen as a Clean and Sustainable Energy Vector for Global Transition from Fossil-Based to Zero-Carbon

Design of a new nanocomposite based on Keggin-type [ZnW12O40]6- anionic cluster anchored on NiZn2O4 ceramics as a promising material towards the electrocatalytic hydrogen storage

Extensive research efforts have been dedicated to developing electrode materials with high capacity to address the increasing complexities arising from the energy crisis. Herein, a new nanocomposite was synthesized via the sol-gel method by immobilizing K6ZnW12O40 within the surface of NiZn2O4. ZnW12O40@NiZn2O4 was characterized by FT-IR, UV-Vis, XRD, SEM, EDX, BET, and TGA-DTG methods. The electrochemical characteristics of the materials were examined using cyclic voltammogram (CV) and charge-discharge chronopotentiometry (CHP) techniques. Multiple factors affecting the hydrogen storage capacity, including current density (j), surface area of the copper foam, and the consequences of repeated cycles of hydrogen adsorption-desorption were evaluated. The initial cycle led to an impressive hydrogen discharge capability of 340 mAh/g, which subsequently increased to 900 mAh/g after 20 cycles with a current density of 2 mA in 6.0 M KOH medium. The surface area and the electrocatalytic characteristics of the nanoparticles contribute to facilitate the formation of electrons and provide good diffusion channels for the movement of electrolyte ions throughout the charge-discharge procedure.

Physics-informed NN-based adaptive backstepping terminal sliding mode control of buck converter for PEM electrolyzer

This paper proposes an advanced control approach to controlling a DC-DC buck converter for a proton exchange membrane (PEM) electrolyzer within the framework of a direct current (DC) microgrid. The proposed adaptive backstepping terminal sliding mode control (ABTSMC) leverages a physics-informed neural network (PINN) to accurately estimate and compensate for system uncertainty. The composite controller achieves finite-time convergence of the tracking error by combining backstepping control and terminal sliding mode control (TSMC). The proposed PINN aims to optimize the unconstrained parameters by utilizing observed training points from the solution, ensuring the network accurately interpolates a limited portion of the solution. The efficacy of the proposed hybrid control method is validated using a hardware-in-the-loop (HIL) implementation under various test settings, ensuring the preservation of the actual performance of the PEM electrolyzer during testing. The experimental verification results demonstrate that the proposed control method exhibits greater benefits, such as a faster dynamic response and greater robustness against parameter uncertainties than improved sliding mode-based controllers. In situations where operational conditions change, a rapid response is achieved within a mere 0.025 s of settling time, exhibiting a minimal percentage overshoot of about 17.5 % and presenting minimal fluctuations.

Advanced (photo)electrocatalytic approaches to substitute the use of fossil fuels in chemical production

Electrification of the chemical industry for carbon-neutral production requires innovative (photo)electrocatalysis. This study highlights the contribution and discusses recent research projects in this area, which are relevant case examples to explore new directions but characterised by a little background research effort. It is organised into two main sections, where selected examples of innovative directions for electrocatalysis and photoelectrocatalysis are presented. The areas discussed include (i) new approaches to green energy or H2 vectors, (ii) the production of fertilisers directly from the air, (iii) the decoupling of the anodic and cathodic reactions in electrocatalytic or photoelectrocatalytic devices, (iv) the possibilities given by tandem/paired reactions in electrocatalytic devices, including the possibility to form the same product on both cathodic and anodic sides to "double" the efficiency, and (v) exploiting electrocatalytic cells to produce green H2 from biomass. The examples offer hits to expand current areas in electrocatalysis to accelerate the transformation to fossil-free chemical production.

Thermally constructed stable Zn-doped NiCoOx-z alloy structures on stainless steel mesh for efficient hydrogen production via overall hydrazine splitting in alkaline electrolyte

Hydrogen has a high energy density of approximately 120 to 140 MJ kg^-1, which is very high compared to other natural energy sources. However, hydrogen generation through electrocatalytic water splitting is a high electricity consumption process due to the sluggish oxygen evolution reaction (OER). As a result, hydrogen generation through hydrazine-assisted water electrolysis has recently been intensively investigated. The hydrazine electrolysis process requires a low potential compared to the water electrolysis process. Despite this, the utilization of direct hydrazine fuel cells (DHFCs) as portable or vehicle power sources necessitates the development of inexpensive and effective anodic hydrazine oxidation catalysts. Here, we prepared oxygen-deficient zinc-doped nickel cobalt oxide (Zn-NiCoO_x-z) alloy nanoarrays on stainless steel mesh (SSM) using a hydrothermal synthesis method followed by thermal treatment. Furthermore, the prepared thin films were used as electrocatalysts, and the OER and hydrazine oxidation reaction (HzOR) activities were investigated in three- and two-electrode systems. In a three-electrode system, Zn-NiCoO_x-z/SSM HzOR requires -0.116 V (vs RHE) potential to achieve a 50 mA cm^-2 current density, which is dramatically lower than the OER potential (1.493 V vs RHE). In a two-electrode system (Zn-NiCoO_x-z/SSM(-)∥Zn-NiCoO_x-z/SSM(+)), the overall hydrazine splitting potential (OHzS) required to reach 50 mA cm^-2 is only 0.700 V, which is dramatically less than the required potential for overall water splitting (OWS). These excellent HzOR results are due to the binder-free oxygen-deficient Zn-NiCoO_x-z/SSM alloy nanoarray, which provides a large number of active sites and improves the wettability of catalysts after Zn doping.

Development of Digested Sludge-Assimilating and Biohydrogen-Yielding Microflorae

Digested sludge (DS) is a waste product of anaerobic digestion that is produced during the biodegradation of excess sludge. It cannot be used as a substrate for further biogas production owing to its recalcitrant nature. In the present study, we used a heat treatment technique to convert DABYS microflora (DABYS = digested sludge-assimilating and biogas-yielding soil microflora), which degraded DS and produced methane gas, to a microflora that could produce hydrogen gas from DS. Heat treatment at 80 and 100 °C inactivated the methanogens that consume hydrogen for methane production but did not affect the thermotolerant bacteria. We developed three microflorae (DABYS-A80, DABYS-A100, and DABYS-80B) to exclusively produce hydrogen gas. They included representatives from the anaerobic eubacterial families Clostridiaceae and Enterobacteriaceae. Pseudomonas sp. was also present in DABYS-A80 and DABYS-A100. It is thought that bacteria in the Enterobacteriaceae family or Pseudomonas genus survive heat treatment because they are embedded in microgranules. Enzymatic analysis suggested that the microflorae hydrolyzed DS using cellulase, chitinase, and protease. Under optimum culture conditions, DABYS-A80, -A100, and B-100 produced gas yields of 8.0, 7.1, and 2.6 mL, respectively, from 1.0 g of dried DS.

Modeling, Degradation Study, Failures Diagnosis and Faulty Operating Management of Electrolyzers

Hydrogen is considered an effective solution to deliver or store energy [...].

Stability Tests on Anion Exchange Membrane Water Electrolyzer under On-Off Cycling with Continuous Solution Feeding

In this study, the stability of an anion exchange membrane water electrolyzer (AEMWE) cell was evaluated in an on-off cycling operation with respect to an applied electric bias, i.e., a current density of 500 mA cm−2, and an open circuit. The ohmic and polarization resistances of the system were monitored during operation (~800 h) using electrochemical impedance spectra. Specific consideration was given to the ohmic resistance of the cell, especially that of the membrane under on-off cycling conditions, by consistently feeding the cell with KOH solution. Owing to an excess feed solution, a momentary increase in the polarization resistance was observed immediately after the open-circuit. The excess feed solution was mostly recovered by subjecting the cell to the applied electric bias. Stability tests on the AEMWE cell under on-off cycling with continuous feeding even under an open circuit can guarantee long-term stability by avoiding an irreversible increase in ohmic and polarization resistances.

A Comprehensive Survey of Alkaline Electrolyzer Modeling: Electrical Domain and Specific Electrolyte Conductivity

Alkaline electrolyzers are the most widespread technology due to their maturity, low cost, and large capacity in generating hydrogen. However, compared to proton exchange membrane (PEM) electrolyzers, they request the use of potassium hydroxide (KOH) or sodium hydroxide (NaOH) since the electrolyte relies on a liquid solution. For this reason, the performances of alkaline electrolyzers are governed by the electrolyte concentration and operating temperature. Due to the growing development of the water electrolysis process based on alkaline electrolyzers to generate green hydrogen from renewable energy sources, the main purpose of this paper is to carry out a comprehensive survey on alkaline electrolyzers, and more specifically about their electrical domain and specific electrolytic conductivity. Besides, this survey will allow emphasizing the remaining key issues from the modeling point of view.

Zirconia Toughened Alumina-Based Separator Membrane for Advanced Alkaline Water Electrolyzer

Hydrogen is nowadays considered a favorable and attractive energy carrier fuel to replace other fuels that cause global warming problems. Water electrolysis has attracted the attention of researchers to produce green hydrogen mainly for the accumulation of renewable energy. Hydrogen can be safely used as a bridge to successfully connect the energy demand and supply divisions. An alkaline water electrolysis system owing to its low cost can efficiently use renewable energy sources on large scale. Normally organic/inorganic composite porous separator membranes have been employed as a membrane for alkaline water electrolyzers. However, the separator membranes exhibit high ionic resistance and low gas resistance values, resulting in lower efficiency and raised safety issues as well. Here, in this study, we report that zirconia toughened alumina (ZTA)-based separator membrane exhibits less ohmic resistance 0.15 Ω·cm2 and low hydrogen gas permeability 10.7 × 10-12 mol cm-1 s-1 bar-1 in 30 wt.% KOH solution, which outperforms the commercial, state-of-the-art Zirfon® PERL separator. The cell containing ZTA and advanced catalysts exhibit an excellent performance of 2.1 V at 2000 mA/cm2 at 30 wt.% KOH and 80 °C, which is comparable with PEM electrolysis. These improved results show that AWEs equipped with ZTA separators could be superior in performance to PEM electrolysis.