Sustainable Hydrogen Research Articles

Harnessing Ti3C2-WS2 nanostructures as efficient energy scaffoldings for photocatalytic hydrogen generation

Two-dimensional (2D) Ti3C2 MXene have attracted a lot of attention as frontier materials for the development of effective photocatalysts that can transform solar energy into chemical energy, which is essential for water splitting to produce hydrogen. Here, we use first principle calculations to understand the structural, electronic, and vibrational features of a novel heterostructure comprising a monolayer of tungsten disulfide (WS2) and titanium carbide (Ti3C2) MXene. Our theoretical calculations revealed that the Ti3C2 maximizes the interfacial contact area with the WS2 monolayer creating a strong p–-d hybridization for the WS2/Ti3C2 heterostructure. As a result, a well-constructed Schottky junction is enabled, facilitating an interconnected electron pathway across the interface which is conducive for an efficient photocatalytic performance. Further, the experimentally designed WS2/Ti3C2 heterostructure and its photocatalytic activity based on the synergistic action between MXene and WS2 is investigated. Optical properties calculated are compared with experimental data derived from UV–Visible spectroscopy. The excellent conductivity and stability along with the light absorption in the visible region of WS2/Ti3C2 enhances the photocatalytic performance approaching photocurrent densities of ∼33 and 120 μA/cm2 in the HER and OER region, respectively. Overall, the present research not only improves our understanding of WS2/Ti3C2 heterostructure for an improved photocatalytic activity, but also provides an efficient method toward sustainable hydrogen production.

Strong electron coupling effect of non-precious metal Schottky junctions enhanced square meter level photocatalytic hydrogen evolution

Photocatalytic hydrogen production technology utilizes solar energy to decompose water into hydrogen, helping to alleviate the pressure of energy depletion. Engineering of non-precious metal nanomaterials as cocatalysts can play a significant role in low-cost, sustainable, and large-scale photocatalytic hydrogen production. Herein, MnCdS-Vs/NiCo2S4 (MCSN) Schottky junction nanomaterials with strong electron coupling effect were prepared by a two-step hydrothermal method and successfully applied to a square meter hydrogen evolution device. The optimized MCSN material demonstrated high hydrogen evolution activity of 34.28 mmol g−1 h−1, which is 9.34 and 685.60 times higher than that of pure MnCdS-Vs and NiCo2S4, respectively. More importantly, in a square meter (1 m2) flat-plate reactor, MCSN produced H2 evolution approximately 201 mmol in 5 h, showcasing its potential for large-scale applications. In-situ XPS and DFT calculations demonstrated that MnCdS-Vs interacts with NiCo2S4 to produce a strong electron coupling effect and form a Schottky junction. It promotes the facilitated the directional migration of photogenerated electrons from MnCdS-Vs to NiCo2S4, but also effectively suppressed electron backflow through the Schottky barrier. Furthermore, the abundance of sulfur vacancies enhanced visible light absorption capability, further improving photocatalytic hydrogen evolution performance. This work delves into the role of defect engineering and Schottky junction design in enhancing photocatalytic performance, providing new insights into transitioning photocatalytic hydrogen production technologies from small-scale laboratory experiments to large-scale practical applications.

Fabrication and characterization of rippled graphene/LDPE composites with enhanced hydrogen barrier properties

Hydrogen plays a pivotal role as a sustainable energy carrier, but the cost-effective and efficient production of gas barrier materials for hydrogen storage still poses a considerable challenge. In this research, we investigate the hydrogen barrier properties of nanocomposites based on low-density polyethylene (LDPE) filled with varying concentrations (0–5 wt%) of rippled graphene. The low-density polyethylene rippled graphene (LPRG) nanocomposites were prepared by drop-casting a suspension of graphene with LDPE dissolved in Toluene, which resulted in a uniform dispersion of rippled graphene within the LDPE matrix. Mechanical testing revealed notable improvements in tensile strength (+40%) and Young's modulus (+120%), confirming the reinforcing effect of rippled graphene in the polymer matrix. Results from the thermogravimetric analysis showed that the addition of rippled graphene significantly increased the thermal stability of the material, reporting an increase of 77 °C in the thermal degradation temperature at a nanofiller loading of 1 wt%. Additionally, the incorporation of rippled graphene in the composite improved the thermal conductivity by 161 %. Moreover, it resulted in an electrically percolated network at a critical nanofiller loading of 1 wt%, contributing to enhanced electrostatic discharge safety. Finally, gas permeability tests unveiled a 50% reduction in hydrogen permeability of LPRG with graphene content of 5 wt% compared to pristine LDPE, making graphene/LDPE composites a superior choice for sustainable and efficient hydrogen storage applications.

Physical insight into the enhanced urea electrooxidation using Ni and Fe-based LDH, LDO, and hydroxides under different dissolved gas saturation conditions in electrolyte

The production of green hydrogen is one of the most demanding and challenging for modern technology. A promising and an effective approach is electrocatalytic anodic urea oxidation reaction to generate hydrogen at cathode under alkaline electrolysis condition. However, it remains crucial for the development of active and stable electrocatalysts for efficient urea oxidation. In this study, we employed the hydrothermal synthesis route for NiFe LDH, NiFe LDO, and Ni(OH)2. The superior performance of NiFe LDH compared to other catalysts is observed due to easy charge transfer facilitated by Fe ions. Moreover, Fe incorporation prevents surface poisoning of the electrocatalyst, resulting in increased activity and stability for electrocatalytic urea oxidation reaction. The influence of different electrolyte environments on the performance of urea-based electrolyzers for sustainable hydrogen production and management of urea-rich wastewater has been measured for the first time by varying oxygen saturation and nitrogen purging conditions. In cyclic voltammetry studies, O2-saturated and purging conditions outperformed N2 gas saturation or purging. The findings of this study provide valuable insight into the design of practical and environmentally friendly urea electrooxidation systems.

Sustainable hydrogen through decomposition of ammonia and its derivatives by thermochemical processes: a review

Sustainable hydrogen through decomposition of ammonia and its derivatives by thermochemical processes: a review

Catalysts for Sustainable Hydrogen Production: Preparation, Applications and Process Integration, 2nd Edition

The effects of climate change are now evident all over the world [...]

Hydrogen Energy in Electrical Power Systems: A Review and Future Outlook

Hydrogen energy, as a zero-carbon emission type of energy, is playing a significant role in the development of future electricity power systems. Coordinated operation of hydrogen and electricity will change the direction and shape of energy utilization in the power grid. To address the evolving power system and promote sustainable hydrogen energy development, this paper initially examines hydrogen preparation and storage techniques, summarizes current research and development challenges, and introduces several key technologies for hydrogen energy application in power systems. These include hydrogen electrification technology, hydrogen-based medium- and long-term energy storage, and hydrogen auxiliary services. This paper also analyzes several typical modes of hydrogen–electricity coupling. Finally, the future development direction of hydrogen energy in power systems is discussed, focusing on key issues such as cost, storage, and optimization.

Highly Efficient CoFeP Nanoparticle Catalysts for Superior Oxygen Evolution Reaction Performance.

Developing effective and long-lasting electrocatalysts for oxygen evolution reaction (OER) is critical for increasing sustainable hydrogen production. This paper describes the production and characterization of CoFeP nanoparticles (CFP NPs) as high-performance electrocatalysts for OER. The CFP NPs were produced using a simple hydrothermal technique followed by phosphorization, yielding an amorphous/crystalline composite structure with improved electrochemical characteristics. Our results reveal that CFP NPs have a surprisingly low overpotential of 284 mV at a current density of 100 mA cm-2, greatly exceeding the precursor CoFe oxide/hydroxide (CFO NPs) and the commercial RuO2 catalyst. Furthermore, CFP NPs demonstrate exceptional stability, retaining a constant performance after 70 h of continuous operation. Post-OER characterization analysis revealed transformations in the catalyst, including the formation of cobalt-iron oxides/oxyhydroxides. Despite these changes, CFP NPs showed superior long-term stability compared to native metal oxides/oxyhydroxides, likely due to enhanced surface roughness and increased active sites. This study proposes a viable strategy for designing low-cost, non-precious metal-based OER catalysts, which will help advance sustainable energy technology.

Boosting green hydrogen production with ZnS@MoS2 2D materials: A structural, electrochemical and photocatalytic analysis

Sustainable green hydrogen production and utilization is one of the serious options to net-zero emission and to mitigate climate change. Herein, a range of techniques has been employed to extricate structural alterations and assess electrochemical (EC) and photocatalytic (PC) properties of MoS2 and ZnS deposited MoS2 (ZnS@MoS2) 2D Materials for green hydrogen production. These 2D materials were explored via a simple hydrothermal method. X-Ray Diffraction (XRD) analysis of ZnS@MoS2 2D materials disclosed significant structural transformations, attributed to ZnS deposition, evident through peak shifts and the emergence of new peaks. Scanning electron microscopy (SEM) images revealed distinct flower-like, petal-arranged formations in MoS2 and ZnS@MoS2, while as high-resolution transmission electron microscopy (HR-TEM) images provided insights into the nanoscale structure and the d‐spacing of MoS2 and ZnS@MoS2 materials. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were utilized to determine elemental composition, chemical states, and structural characteristics. Electrochemical assessments showed that MoS2 exhibited a hydrogen evolution reaction (HER) with an onset potential of −0.3 V, whereas ZnS@MoS2 demonstrated an improved HER with an onset potential of −0.25 V (relative to Ag/AgCl). Notably, the ultra-low overpotential (η@10) of −0.40 V for MoS2 and −0.30 V for ZnS@MoS2, underlined their exceptional catalytic effectiveness. Moreover, ZnS@MoS2 material accomplished an improved photocatalytic hydrogen evolution rate of 4663.5 µmolh−1g−1, surpassing MoS2’s rate of 3318.85 µmolh−1g−1. In conclusion, it is believed that ZnS@MoS2 material can be a potential candidate for green hydrogen production, not only by splitting ultrapure water but future work will explore the catalyst’s performance in seawater electrolysis.

Floating Photothermal Hydrogen Production.

Solar-to-hydrogen (STH) is emerging as a promising approach for energy storage and conversion to contribute to carbon neutrality. The lack of efficient catalysts and sustainable reaction systems is stimulating the fast development of photothermal hydrogen production based on floating carriers to achieve unprecedented STH efficiency. This technology involves three major components: floating carriers with hierarchically porous structures, photothermal materials for solar-to-heat conversion and photocatalysts for hydrogen production. Under solar irradiation, the floating photothermal system realizes steam generation which quickly diffuses to the active site for sustainable hydrogen generation with the assistance of a hierarchically porous structure. Additionally, this technology is endowed with advantages in the high utilization of solar energy and catalyst retention, making it suitable for various scenarios, including domestic water supply, wastewater treatment, and desalination. A comprehensive overview of the photothermal hydrogen production system is present due to the economic feasibility for industrial application. The in-depth mechanism of a floating photothermal system, including the solar-to-heat effect, steam diffusion, and triple-phase interaction are highlighted by elucidating the logical relationship among buoyant carriers, photothermal materials, and catalysts for hydrogen production. Finally, the challenges and new opportunities facing current photothermal catalytic hydrogen production systems are analyzed.

Breaking the inactivity of MXenes to drive Ampere-level selective oxygen evolution reaction in seawater

The limited activity and stability of conventional anodes in seawater have posed a significant obstacle to sustainable green hydrogen production directly from seawater via electrolysis. To address these challenges, we engineered Ti3C2Tx-MXene by incorporating iron and boron into its matrix (tagged FBT) for selective oxygen evolution reaction (OER). Positioning B underneath the top layer induces charge disparity on the Fe-sites, which influences the subsequent growth of the ZIF-67 metal-organic framework (MOF) on the MXene surface through Fe-O-Co ionic bonds. DFT calculations reveal a favorable binding energy of −2.30 eV at the heterointerface for ZIF-67 adsorption to the surface of FBT via O-Co bond, a shortened bond length of 1.94 Å, confirming the formation of ionic bonds. These ionic bonds tune the active sites for an enhanced and selective OER over chlorine evolution reaction (CER), preventing active Fe species' leaching and ensuring stability at >1.56 A cm−2 in 6 M alkaline seawater over 370 hours. Further, FBT and ZIF-67/FBT require low overpotentials of 521.2 and 508 mV, respectively, to deliver 1 A cm−2 in 6 M alkaline seawater. Our findings demonstrate a robust strategy to significantly expand the potential of MXenes from simple conductive substrates to efficient OER catalysts for seawater splitting and beyond.

Electrochemical performance of in-situ electrodeposited spinel-structured high entropy oxides/NiFeCuMoMn-high entropy alloy multiphase electrocatalysts for seawater electrolysis

Seawater electrolysis plays a pivotal role in advancing sustainable hydrogen production. High entropy alloys (HEAs), an innovative class of materials, have garnered significant attention for seawater electrolysis research in recent years due to their exceptional mechanical strength, catalytic efficiency, and corrosion resistance properties. This study presents the synthesis of a novel Ni-Fe-Cu-Mo-Mn based high entropy alloy catalyst featuring in-situ grown high entropy oxides (HEOs). This material exhibits HER overpotentials of η10 (Overpotential at 10 mA)=50.5 mV in 1 M KOH solution and η10 = 371 mV in natural seawater with a pH ≈ 8.2, after 50 h of Hydrogen evolution reactio (100 mA·cm−2), the η10 in seawater decreased from 371 mV to 343 mV. Demonstrates some autocatalytic capacity. Analytical results indicated that the HEOs/NFCMM (NiFeCuMoMn) -HEA surface is characterized by a spinel structure. The presence of this spinel-structured HEOs layer on the HEOs/NFCMM-HEA catalyst's surface enhances its ability to adsorb H2O effectively and facilitates the desorption of H* from non-acidic electrolytes, thereby significantly boosting the HER process.

Front Cover: Advancements in Biomass‐Derived Activated Carbon for Sustainable Hydrogen Storage: A Comprehensive Review (Chem. Asian J. 16/2024)

Front Cover: Advancements in Biomass‐Derived Activated Carbon for Sustainable Hydrogen Storage: A Comprehensive Review (Chem. Asian J. 16/2024)

A strategy to reutilize silver nanoparticles on silicon nanowires via photocathodic activation for enhanced and sustainable hydrogen evolution

The development of electrodes for hydrogen evolution via water splitting in a neutral electrolyte is highly desirable, especially considering that natural water resources such as seawater typically have a neutral pH. In this study, silicon nanowires (SiNWs) arrays with uniform silver (Ag) decoration are prepared as a cathode material, which exhibits excellent and stable electrochemical performance for neutral water electrolysis. Ag ions, utilized in the preparation of SiNWs through metal-assisted chemical etching technique, are retained and decorated within the SiNWs array without undergoing a dissolution process, referred to as Native SiNWs. Remained Ag+ ions on the SiNWs are activated photocathodically and reduced to Ag0, resulting in a significantly enhanced performance as an electrocatalyst for hydrogen evolution reaction (HER). Hence, this photocathodic activation of Native SiNWs (PCA-Native SiNWs) eliminates the need for additional cocatalyst deposition for HER, utilizing the Ag ions employed in the SiNWs preparation process. This enhancement in HER activity is exclusively observed by photocathodic activation, not by cathodic activation without light irradiation, indicating the crucial role of photoelectrons in SiNWs under light irradiation for the activation. Additionally, the nanowire structure serves as an ideal platform for Ag nanoparticles, providing sufficient surface area, resulting in excellent dispersion and an increased number of active sites. Furthermore, PCA-Native SiNWs demonstrates outstanding electrochemical stability for over 60 h, with no significant reduction in current density or structural degradation in a neutral electrolyte. Several characterizations and electrochemical analyses have been conducted to elucidate the in-situ decoration of Ag nanoparticles on SiNWs and investigate the surface chemistry for the activation mechanism. This work introduces a new perspective on using Ag-decorated SiNWs directly as an electrocatalyst for effective hydrogen evolution in a neutral media.

Boosting HER performance of ZIF-67 via optimizing synthesis parameters in alkaline medium

Electrochemical water splitting offers a promising route to sustainable hydrogen production. Metal-Organic Frameworks (MOFs) have emerged as potential electrocatalysts due to their tunable structure and composition. We investigated the electrocatalytic activity of ZIF-67 for the hydrogen evolution reaction (HER) in alkaline media. Synthesis parameters, including temperature, reaction time, acidity, molar ratio of 2-methylimidazole (2-MIM) to cobalt source, cobalt source type, addition method of 2-MIM, and solvent type, were systematically varied to optimize the electrocatalytic properties of ZIF-67. The synthesized ZIF-67 electrocatalysts were characterized using BET, FESEM, EDS, TEM, XRD, FTIR, and UV–vis spectroscopy. The electrocatalytic properties were evaluated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and chronoamperometry methods. The optimized ZIF-67 electrocatalyst exhibited remarkable performance, with a low overpotential of 171 mV, a small Tafel slope of 82 mV.dec−1, a low charge transfer resistance of 97 Ω, a high double-layer capacitance of 13.5 mF cm−2, and high stability for 15 h at the current density of 10 mA cm−2. The enhanced electrocatalytic activity of the optimized ZIF-67 was attributed to its high surface area, tunable pore structure, and the presence of active cobalt sites.

Zr and Mo doping to modulate the electronic structure of Ni3S2 for OER electrocatalysis

To enter the era of a clean and sustainable hydrogen economy, it is crucial to first discover non-precious metal electrocatalysts that can be used for oxygen evolution reaction (OER) in electrochemical water splitting. In this work, highly active and durable Zr and Mo co-doped Ni3S2 catalyst (ZrMo–Ni3S2/NF) loaded on Ni foams for OER in alkaline media were prepared using a simple one-step hydrothermal method. The resulting nanocomposites were characterized by various methods and evaluated for their electrocatalytic performance towards OER. The ZrMo–Ni3S2/NF nanocomposite exhibites excellent OER electrocatalytic activity with a low overpotential of 257 mV at a current density of 10 mA cm−2 as well as an excellent electrochemical stability, showing only a slight decay during the 70 h test period. The remarkable electrocatalytic performance of the ZrMo–Ni3S2/NF electrode is attributed to the synergistic strong electronic interaction between the co-doped Zr and Mo. This work not only demonstrates a highly electrocatalytic active OER catalyst for water splitting, but also provides a new perspective on the development of highly active OER catalysts through doping strategies.

Breaking the trade-off between proton conductivity and mechanical stability through liquid-crystal-modified aramid fibers in sulfonated polyether ether ketone membranes

In the quest for sustainable and high-performance hydrogen fuel cells, proton exchange membranes (PEMs) stand as a pivotal research focus. To overcome the significant challenge posed by the traditional trade-offs between proton conductivity and mechanical stability, this work introduces liquid-crystal-modified aramid fibers (DBAF) with highly ordered molecular arrangements and abundant sulfonic acid groups on the side chains as proton-hopping sites into a sulfonated poly (ether ether ketone) (SPEEK) matrix. The inclusion of components not only improves the proton conductivity of the membrane, but also boosts its mechanical strength. The results of our study demonstrate that the externally attached sulfonic acid groups create extra channels for the transport of protons. Additionally, the organized and consistently stable hydrogen-bond network enables the Grotthuss transport mechanism within the SPEEK membrane. The 1 wt% DBAF-SPEEK composite membrane exhibits a maximum proton conductivity of 0.23 S cm−1 at 80 °C, representing a 64% increase over the baseline SPEEK membrane's 0.14 S cm−1. Simultaneously, the tensile strength at normal room temperature is 39.7 MPa, exhibiting an improvement of 86% compared to the initial value of 21.3 MPa. Additionally, the swelling ratio is lowered by 18.69%. Compared with the baseline membrane, the DBAF-enhanced SPEEK composite membrane exhibits superior mechanical stability and proton conductivity within a moderate temperature range (30–80 °C). Consequently, this work offers valuable insights for the development of novel proton-conductive materials.

Bubble-Guidance Breaking Gas Shield for Highly Efficient Overall Water Splitting.

Overall water splitting is a promising technology for sustainable hydrogen production, but the primary challenge is removing bubbles from the electrode surface quickly to increase hydrogen production. Inspired by the directional fluid transport properties of natural biological surfaces like Nepenthes peristome and Morpho butterfly's wings, here a strategy is demonstrated to achieve highly efficient overall water splitting by a bubble-guidance electrode, that is, an anisotropic groove-micro/nanostructured porous electrode (GMPE). Gradient groove micro/nanostructures on the GMPE serve as high-speed bubble transmission channels and exhibit superior bubble-guidance capabilities. The synergistic effect of the asymmetric Laplace pressure generated between microscale porous structure and groove patterns and the buoyancy along the groove patterns pushes the produced bubbles directionally to spread, transport, and detach from the electrode surface in time. Moreover, the low adhesive nanosheet arrays are beneficial to reduce bubble size and increase bubble release frequency, which cooperatively improve mass transfer with the microscale structure. Notably, GMPE outperforms planar-micro/nanostructured porous electrode (PMPE) in hydrogen/oxygen evolution reactions, with GMPE||GMPE showing better water splitting performance than commercially available RuO2||20 wt.% Pt/C. This work improves electrodes for better mass transfer and kinetics in electrochemical reactions at solid-liquid-gas interfaces, offering insight for designing and preparing gas-involved photoelectrochemical electrodes.

Electrodeposition of Nickel–Molybdenum–Phosphide on copper foam electrode for efficient hydrogen evolution reaction

In the quest for efficient and cost-effective catalysts to drive the hydrogen evolution reaction (HER) in electrochemical water splitting, copper foam (CuF) is a favorable candidate for electrode coating. Precious metal catalysts like Pt/C dominate the field but must be improved because of their high cost and scarcity. Therefore, we have synthesized and evaluated a sequence of nickel-originated electrocatalysts (Ni, NiMo, NiP, and NiMoP) with the electrodeposition of CuF to facilitate substantial improvements in HER performance. Herein, the Ni–Mo–P ternary system, owing to its desirable electronic structure and catalytic mechanism, contributes to enhancing the thermodynamics and kinetics of the HER. Performance analysis reveals that all studied catalysts follow the order of Ni/CuF > NiMo/CuF > NiP/CuF > NiMoP/CuF regarding both the Tafel slope and overpotential. Hence, the top performer, NiMoP/CuF, exhibits tremendous thermodynamics with an η10 = 159 mV and Tafel slope kinetics of 126.66 mV·dec⁻1 at 1.0 M KOH in water splitting. Overall, this report presents a well-capable way of optimizing the electrocatalytic function and stability of CuF-electro-coated catalysts for the HER. This research opens new avenues for cost-effective, stable, and efficient HER catalysts, showcasing the potential of NiMoP/CuF in advancing sustainable hydrogen production technologies.

Tungsten-needle intensifies microwave-sustained plasma accelerating direct H2S conversion to H2

Direct sustainable conversion of hydrogen sulfide (H2S) enables collaborative recovery of H and S resources via a metal-enhanced microwave plasma strategy, avoiding the hydrogen waste in the traditional Claus process. However, the metal size effect on microwave plasma property, the optimal process parameters, and the enhancement mechanism remain unclear in H2S conversion. Herein, the optimal tungsten needle (diameter: 1 mm, length: 60 mm, and tip angle: 10°) is experimentally proven for intensifying microwave discharge in multi-mode cavities. Theoretical calculations and plasma distribution reveal that the optimized tungsten needle achieves the ideal coupling with the microwave field, exhibiting extreme electric field augmentation around the needle tip. Tungsten-needle intensifies microwave-sustained plasma, realizing 40.2 % (90.1 %) conversion of 100 % (10 %) concentration H2S to H2 at a low microwave power of 300 W with a good stability of 30 hrs. Low power, large flow rate, and high H2S concentration are beneficial for improving energy efficiency. The excitation of microwave plasma is accompanied by a massive generation of highly energetic electrons. The direct high-energy electron-H2S collision contributes a lot to H2S splitting, especially for high-concentration H2S. In-situ optical emission spectroscopy confirms the vital S and H radicals in the plasma. The free radical reactions triggered by electron collisions are responsible for the production of H2 and S. This work opens an avenue to sustainable and low-carbon hydrogen production from the direct conversion and utilization of H2S.