High-efficiency Hydrogen Production Research Articles

Novel Organic Dibranched Photosensitizers Featuring Spiro-fluorene for Efficient Hydrogen Generation from Water

Four new metal-free organic photosensitizers featuring either a mono-anchoring donor–π–acceptor (D–π–A) or di-anchoring donor–(π–acceptor)2 (D(–π–A)2) architecture containing a spirobifluorene or spiro[fluorene-9,9’-xanthene] central donor core was prepared. These photosensitizers were subsequently tested for their efficiency in the photocatalytic production of H2, in combination with a Pt/TiO2 catalyst. Additionally, electrochemical, photophysical, and computational studies were conducted. The computational studies were specifically carried out to ascertain the electronic distribution within the photosensitizers. The influence of the molecular design on the efficiency of H2 production was examined. The di-anchoring photosensitizers notably amplified the spectral response in the visible light region, reduce aggregation on TiO2 and enhanced charge transfer. Among the fabricated photocatalytic systems, the di-anchoring photosensitizers exhibited superior photocatalytic efficiency compared to their mono-anchoring counterparts. Among all the photosensitizers, the spiro[fluorene-9,9’-xanthene]-based di-anchoring photosensitizer X2 possessing photocatalytic system demonstrated remarkable performance, producing 406.3 μmol (10.07 mL) of hydrogen over a period of 47 hours under blue light irradiation. This performance corresponds to a turnover number (TON) of 6674, a turnover frequency (TOFi) of 445 h-1, an initial hydrogen production activity (activityi) of 278140 and an apparent quantum yield (AQYi%) of 4.762. The bulky spiro[fluorene-9,9’-xanthene] component endowed the photosensitizers with photostability, as confirmed by their high hydrogen production efficiency over 152 hours of extended irradiation, yielding 12.69 mL of hydrogen. This study revealed, for the first time, that the bulky spiro-fluorene structure contributes positive synergistic effects to hydrogen production. It demonstrates that dibranched photosensitizers containing spiro-fluorene are promising candidates for achieving high and stable hydrogen production activity.

Research on Hybrid Rectifier for High Power Electrolytic Hydrogen Production Based on Modular Multilevel Converter

Aiming at the problem that silicon-controlled rectifiers (SCR) and pulse width modulation (PWM) rectifiers cannot balance high power levels, high hydrogen production efficiency, and high grid connected quality in the current research on rectifier power supplies for electrolytic hydrogen production, a new hybrid rectifier topology based on a modular multilevel converter (MMC) is proposed. The hybrid topology integrates a silicon-controlled rectifier (SCR) with an auxiliary power converter, wherein the SCR is designated as the primary power source for electrolytic hydrogen production. The auxiliary converter employs a cascaded modular multilevel converter (MMC) and an input-series-output-parallel (ISOP) phase-shifted full-bridge (PSFB) arrangement. This configuration allows the auxiliary converter to effectively mitigate AC-side harmonics and minimize DC-side ripple, concurrently transmitting a small amount of power. The effectiveness of the hybrid rectifier in achieving low ripple and harmonic distortion outputs was substantiated through hardware-in-the-loop experiments. Notably, the hybrid topology is characterized by its enhanced electric-to-hydrogen conversion efficiency, elevated power density, cost efficiency, and improved grid compatibility.

Synthesis of Co0·52Cu0·48/Cu@S–C arrays for the enhanced performance of hydrazine-assisted hydrogen production

The development of efficient bifunctional catalysts is the key technology to replace oxygen evolution reaction (OER) with hydrazine oxidation reaction (HzOR) with lower theoretical potential to achieve high efficiency and energy-saving hydrogen production. In this work, the Co0·52Cu0·48/Cu@S–C (−1.3 V) composite with flower-like array was prepared by two-step electrodeposition coupled pyrolysis method. The electrochemical measurements showed that the driving voltages of the optimal composite for HzOR and hydrogen evolution reaction (HER) are respectively −118 mV and 47 mV at a current density (j) of 10 mA cm−2. The excellent performance of Co0·52Cu0·48/Cu@S–C (−1.3 V) composite is attributed to the fact that the flower-like structure exposes more active areas and facilitates the diffusion of electrolyte, the strong electron interaction between Co0·52Cu0·48/Cu and S–C substrate, which can be verified by X-ray photoelectron spectroscopy (XPS), enhances the electrical conductivity, the Co0·52Cu0·48/Cu heterogeneous interface reduces the water dissociation barrier and facilitates the dehydrogenation kinetics of N2H4 determined by density functional theory (DFT) calculations. Due to the excellent performance of Co0·52Cu0·48/Cu@S–C (−1.3 V), the overall hydrazine splitting (OHzS) electrolytic cell was constructed with Co0·52Cu0·48/Cu@S–C (−1.3 V) as electrodes. The results showed the voltages required by the cell are 36, 210 and 282 mV at the current density values of 10, 100 and 200 mA cm−2 respectively, showing that Co0·52Cu0·48/Cu@S–C (−1.3 V) can be used for energy-saving hydrogen production by hydrazine assisted water electrolysis.

Nano core-shell Mn0.5Cd0.5S@ copper phthalocyanine heterojunction structured with high hydrogen production efficiency

The core-shell structure photocatalysts have attracted extensive attention in photocatalysis due to large contact area, multiple reaction sites and high photocatalytic performance. Herein, a series of Mn0.5Cd0.5S@CuPc nano core-shell composites photocatalyst were successfully synthesized by facile solution method. The results showed that the as-prepared Mn0.5Cd0.5S photocatalyst hydrogen evolution was only 0.40 mmol/g·h, while Mn0.5Cd0.5S@CuPc composites show strong light absorption from 600 nm to 800 nm and high catalytic performance compared with pure Mn0.5Cd0.5S. Notably, the hydrogen evolution of Mn0.5Cd0.5S @CuPc-5% reached up to 2.14 mmol/(g·h), representing a remarkable 5.35 times improvement compared to the pure Mn0.5Cd0.5S when the optimal loading capacity of CuPc was set at 5%. The Mn0.5Cd0.5S@CuPc-5% exhibits excellent photocatalytic performance can be attributed to the CuPc forms a uniform molecular film on the surface of Mn0.5Cd0.5S, and the close contact between Mn0.5Cd0.5S and CuPc which can effectively promote the transfer and separation of photo-generated carriers. Moreover, the 5% Mn0.5Cd0.5S@CuPc nano core-shell composites have excellent stability, photocatalyst hydrogen activity reduce was approximately 20.1% after four runs for 12 h. This nano core-shell structure photocatalyst research offers a new strategy for constructing organic-inorganic nanocomposite photocatalysts.

Tailoring microwave frequencies for high-efficiency hydrogen production from biomass

Generating green hydrogen through biomass thermochemical conversion is pivotal for contributing to carbon neutrality. However, the efficiency of hydrogen production is hindered by the byproduct of tar formed during biomass depolymerization. This study employed a variable-frequency microwave ranging from 2430 to 6000 MHz to investigate the influence of microwave frequency on tar removal and hydrogen recovery over activated charcoal (AC). Experimental results indicated that microwave frequencies significantly impact the temperature distribution and heating rates of AC. Notably, at 4640 MHz the AC rapidly reached 1145 °C within seconds, with an instantaneous heating rate of 2022 °C/min. The ultra-fast heating rate crucially contributes to achieving 100 % efficiency in tar cracking, resulting in a hydrogen yield of 32.8 mmol/g. With a hydrogen recovery rate surpassing 94 %, the 4640 MHz frequency represents a 15.4-fold increase compared to the conventional 2450 MHz. This innovative approach holds significant promise for enhancing energy efficiency in the pursuit of carbon-neutral energy production.

Hollow Cu2-xS@NiFe Layered Double Hydroxide Core-Shell S-Scheme Heterojunctions with Broad-Spectrum Response and Enhanced Photothermal-Photocatalytic Performance.

Designing a reasonable heterojunction is an efficient path to improve the separation of photogenerated charges and enhance photocatalytic activity. In this study, Cu2-xS@NiFe-LDH hollow nanoboxes with core-shell structure are successfully prepared. The results show that Cu2-xS@NiFe-LDH with broad-spectrum response has good photothermal and photocatalytic activity, and the photocatalytic activity and stability of the catalyst are enhanced by the establishment of unique hollow structure and core-shell heterojunction structure. Transient PL spectra (TRPL) indicates that constructing Cu2-xS@NiFe-LDH heterojunction can prolong carrier lifetime obviously. Cu2-xS@NiFe-LDH shows a high photocatalytic hydrogen production efficiency (5176.93µmolh-1g-1), and tetracycline degradation efficiency (98.3%), and its hydrogen production rate is ≈10-12 times that of pure Cu2-xS and NiFe-LDH. In situ X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) provide proofs of the S-scheme electron transfer path. The S-scheme heterojunction achieves high spatial charge separation and exhibits strong photoredox ability, thus improving the photocatalytic performance.

A novel microbial community restructuring strategy for enhanced hydrogen production using multiple pretreatments and CSTR operation

To achieve rapid enrichment of the targeted hydrogen-producing bacterial population and reconstruction of the microbial community in the biological hydrogen-producing reactor, the activated sludge underwent multiple pretreatments using micro-aeration, alkaline treatment, and heat treatment. The activated sludge obtained from the multiple pretreatments was inoculated into the continuous stirred tank reactor (CSTR) for continuous operations. The community structure alteration and hydrogen-producing capability of the activated sludge were analyzed throughout the operation of the reactor. We found that the primary phyla in the activated sludge population shifted to Proteobacteria, Firmicutes, and Bacteroidetes, which collectively accounted for 96.69% after undergoing several pretreatments. This suggests that the multiple pretreatments facilitated in achieving the selective enrichment of the fermentation hydrogen-producing microorganisms in the activated sludge. The CSTR start-up and continuous operation of the biological hydrogen production reactor resulted in the reactor entering a highly efficient hydrogen production stage at influent COD concentrations of 4000 mg/L and 5000 mg/L, with the highest hydrogen production rate reaching 8.19 L/d and 9.33 L/d, respectively. The main genus present during the efficient hydrogen production stage in the reactor was Ethanoligenens, accounting for up to 33% of the total population. Ethanoligenens exhibited autoaggregation capabilities and a superior capacity for hydrogen production, leading to its prevalence in the reactor and contribution to efficient hydrogen production. During high-efficiency hydrogen production, flora associated with hydrogen production exhibited up to 46.95% total relative abundance. In addition, redundancy analysis (RDA) indicated that effluent pH and COD influenced the distribution of the primary hydrogen-producing bacteria, including Ethanoligenens, Raoultella, and Pectinatus, as well as other low abundant hydrogen-producing bacteria in the activated sludge. The data indicates that the multiple pretreatments and reactor's operation has successfully enriched the hydrogen-producing genera and changed the community structure of microbial hydrogen production.

Si4Al2O2N6 regulating chemical states of Co catalyst for improved hydrogen production from ethanol steam reforming

Tuning the metal-support interaction is a general strategy of regulating the chemical state of catalytic active site for high-efficiency hydrogen production from ethanol steam reforming (ESR) reaction. In this work, a Co catalyst supported on the Si4Al2O2N6 solid solution of Si3N4 and Al2O3 (Co/Si4Al2O2N6) has been developed to effectively catalyze ESR reaction. Our results demonstrate that the Co/Si4Al2O2N6 catalyst exhibits remarkably improved performances as compared with the Co/Si3N4 and Co/Al2O3 catalysts. In the Co/Si4Al2O2N6-catalyzed ESR reaction, ethanol conversion of 97 % has been achieved with hydrogen yield reaching 73 %. Long-time catalytic experiment manifests the Co/Si4Al2O2N6 catalyst possesses excellent durability. X-ray photoelectron spectroscopy (XPS) studies reveal that the enhanced metal-support interaction (MSI) and charge transfer from Si4Al2O2N6 support to Co species in the Co/Si4Al2O2N6 catalyst confer lower valence state on the Co catalyst supported on Si4Al2O2N6, thus promoting the C–C bond cleavage capability, leading to high C1 product yield and boosting the hydrogen-production efficiency. The catalytic mechanism studies explored by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) reveal that the Co/Si4Al2O2N6 exhibits a remarkable preference for C1 products over the Co/Si3N4 and Co/Al2O3 catalysts at low reaction temperature, thus resulting in high hydrogen-production efficiency with excellent catalytic durability.

Homologous heterostructure CdSe/CdS nanoflowers to enhance photocatalytic hydrogen production

The study of nano-heterostructures as light-capturing system applied in photocatalytic water splitting is a current research hotspot. In this study, a simple in situ anion exchange method was proposed for the synthesis of homologous heterostructure CdSe/CdS nanoflowers. Series of CdSe/CdS composites were obtained by controlling the amounts of Se powder. The optimum ratio 5 wt% CdSe loading on CdS nanosheets achieved the maximum H2 production rate of 16.03 mmol g−1 h−1, which was 1.5 times higher than that of pure CdS. Mechanism study with UV–vis DRS, and photoluminescence revealed the excellent photocatalytic property was attributed to the expansion the absorption range of CdS with the introduction of CdSe, the construction of the Z-scheme heterojunction between CdS and CdSe, and the rich catalytic reaction interfacial sites provided by the hierarchical structure with 2D nanosheets and 3D nanoflowers. This work provided the design and synthesis of homologous heterostructure photocatalysts for high efficiency hydrogen production.

Polymer Design Strategies for Alkaline Membrane Water Electrolysis

Water electrolysis is a carbon-free hydrogen production technology, making it a promising candidate to mitigate aggravating climate change. Ion exchange membranes are an essential component of membrane-based water electrolysis, enabling high hydrogen production efficiency through a zero-gap configuration. The recent research efforts to develop anion exchange membranes and electrode ionomers have made significant improvement in durability of alkaline membrane water electrolyzers without sacrificing performance and efficiency. Still, there are several factors related to polymer electrolytes that contribute to the voltage loss for water splitting in the alkaline condition including electrode local pH, the interface between membrane and electrodes, and electrochemical oxidation of ionomers at high potentials. This presentation will provide the state-of-the-art performance of alkaline membrane water electrolyzers with respect to the structure of anion exchange membranes and ionomers. The material design strategies and future directions to develop advanced polymer electrolytes will be discussed for this green hydrogen production technology.Reference: Park, E.J., Arges, C.G., Xu, H., Kim, Y.S. ACS Energy Lett. 2022 , 7, 10, 3447–3457Motz, A.R., Li, D., Keane, A., Manriquez, L.D., Park, E.J., Maurya, S., Chung, H., Fujimoto, C., Jeon, J., Pagels, M.K., Bae, C., Ayers, K.E., Kim, Y.S. Mater. Chem. A 2021 , 9, 22670-22683Matanovic, I., Kim, Y.S. Current Opinion in Electrochemistry 2023 , 38, 101218Leonard, D.P., Lehmann, M., Klein, J.M., Matanovic, I., Fujimoto, C., Saito, T., Kim, Y.S. Advanced Energy Materials 2023 , 13, 2203488

One-Pot Facile Synthesis of ZrO2-CdWO4: A Novel Nanocomposite for Hydrogen Production via Photocatalytic Water Splitting

ZrO2-based nanocomposites are highly versatile materials with huge potential for photocatalysis. In this study, ZrO2-CdWO4 nanocomposites (NC) were prepared via the green route using aqueous Brassica rapa leaf extract, and its photocatalytic water-splitting application was evaluated. Brassica rapa leaf extract acts as a reducing agent and abundant phytochemicals are adsorbed onto the nanoparticle surfaces, improving the properties of ZrO2-CdWO4 nanocomposites. As-prepared samples were characterized by using various spectroscopic and microscopic techniques. The energy of the direct band gap (Eg) of ZrO2-CdWO4 was determined as 2.66 eV. FTIR analysis revealed the various functional groups present in the prepared material. XRD analysis showed that the average crystallite size of ZrO2 and CdWO4 in ZrO2-CdWO4 was approximately 8 nm and 26 nm, respectively. SEM and TEM images suggested ZrO2 deposition over CdWO4 nanorods, which increases the roughness of the surface. The prepared sample was also suggested to be porous. BET surface area, pore volume, and half pore width of ZrO2-CdWO4 were estimated to be 19.6 m2/g. 0.0254 cc/g, and 9.457 Å, respectively. PL analysis suggested the conjugation between the ZrO2 and CdWO4 by lowering the PL graph on ZrO2 deposition over CdWO4. The valence and conduction band edge positions were also determined for ZrO2-CdWO4. These band positions suggested the formation of a type I heterojunction between ZrO2 and CdWO4. ZrO2-CdWO4 was used as a photocatalyst for hydrogen production via water splitting. Water-splitting results confirmed the ability of the ZrO2-CdWO4 system for enhanced hydrogen production. The effect of various parameters such as photocatalyst amount, reaction time, temperature, water pH, and concentration of sacrificial agent was also optimized. The results suggested that 250 mg of ZrO2-CdWO4 could produce 1574 µmol/g after 5 h at 27 °C, pH 7, using 30 vol. % of methanol. ZrO2-CdWO4 was reused for up to seven cycles with a high hydrogen production efficiency. This may prove to be useful research on the use of heterojunction materials for photocatalytic hydrogen production.

Design Principles of Single-Atom Catalysts for Oxygen Evolution Reaction: From Targeted Structures to Active Sites.

Hydrogen production from electrolytic water electrolysis is considered a viable method for hydrogen production with significant social value due to its clean and pollution-free nature, high hydrogen production efficiency, and purity, but the anode oxygen evolution reaction (OER) process is complex and kinetically slow. Single-atom catalysts (SACs) with 100% atom utilization and homogeneous active sites often exhibit high catalytic activity and are expected to be extensively applied. The catalytic performance of OER can be further improved by precise regulation of the structure through electronic effects, coordination environment, heteroatomicdoping, and so on. In this review, the mechanisms of OER under different conditions are introduced, the latest research progress of SACs in the field of OER is systematically summarized, and then the effects of various structural regulation strategies on catalytic performance are discussed, and principles and ideas for the design of SACs for OER are proposed. In the end, the outstanding issues and current challenges in this field are summarized.

Interfacial engineering of hierarchical MoNi4/NiO heterostructure nanosheet arrays as bifunctional electrocatalysts for urea-assisted energy-saving hydrogen production

Employing urea oxidation reaction (UOR) to substitute slow oxygen evolution reaction (OER) is an effective technique to accomplish high-efficiency hydrogen production. The exploitation of inexpensive and highly active bifunctional catalyst still remains a considerable challenge. We report the hybrid nanosheet arrays constructed of MoNi4/NiO heterojunction with hierarchically crosslinked network architecture by hydrothermal reaction and subsequent annealing process under H2/Ar atmosphere. The special heterostructure with neoteric morphology can promote electron shift and interface interaction through the powerful coupling interface between MoNi4 and NiO, increasing charge transfer speed, intrinsic activity and electrolyte transport. Only 31 mV overpotential and 1.37 V potential are needed to arrive 10 mA cm−2 for hydrogen evolution reaction (HER) and UOR, respectively. For the two-electrode urea-assisted electrolyzer, the lower potential of 1.41 V is required to reach 10 mA cm−2. Moreover, it displays superior stability with unceasing working for 54 h at the cell voltage of 1.41 V without obvious activity degeneration. This research provides an insight on the construct of high-efficiently bifunctional catalyst by synergistic coupling of NiMo-based alloys with metal oxides.

Mutual promotion by structural design and intrinsic activity coupling of CNTs/MoC/CoNiMo for water splitting and urea electrolysis

Construction of durable multi-function electrocatalysts for hydrogen production is still highly challenging. Herein, we report a hierarchical integrated tri-functional heterogeneous CNTs/MoC/CoNiMo electrode for HER and related OER/UOR. The carbon-protected Ni nanoparticles yield abundant γ-NiOOH active intermediates to boost OER/UOR, while DFT calculations verify Mo migration induced by MoC and CoNiMo alloy under negative potentials generates HER super-active sites on Mo-rich surfaces. Additionally, the parallel aligned nanosheets with out-plane extended CNTs arrays can guide the rapid bubbles release and expand the accessible surface area. Therefore, the optimized CNT/MoC/NMC-3 electrode can achieve overpotentials of 51 mV (HER) and 226 mV (OER), with low potential threshold of 1.257 V (UOR) at 10 mA cm–2. Moreover, the assembled symmetric urea electrolyzer reaches a 1.291 V cell voltage at 10 mA cm–2. This work provides a novel strategy for heterostructure multi-component integration for achieving high-efficiency hydrogen production and urea-containing wastewater purification.

Unveiling the origin of activity in RuCoOx-anchored nitrogen-doped carbon electrocatalyst for high-efficiency hydrogen production and hydrazine oxidation using Raman spectroscopy

Hydrazine-assisted water electrolysis has gained much attention nowadays as an energy-saving strategy for the large-scale production of hydrogen fuel. Regardless, the synthesis of highly proficient bifunctional electrocatalysts remains a major challenge. Metal–organic frameworks (MOF) derived electrocatalysts have recently demonstrated excellent bifunctional activity in water electrolysis. Herein, we developed a new type of Ru-MOF on rod-like Co-MOF (Ru/Co-MOF) microstructures via a two-step solvothermal route. Subsequently, the Ru/Co-MOF was used as a precursor and self-template to synthesize an electrocatalytically active RuO2/Co3O4 anchored nitrogen-doped carbon (RuCoOx@NC) composite via a one-pot pyrolysis–oxidation strategy under atmospheric air. The RuCoOx@NC composite showed an ultralow overpotential of 44 mV for the hydrogen evolution reaction and 255 mV for the oxygen evolution reaction at 10 mA cm−2 in a 1 M KOH solution. Besides, the RuCoOx@NC composite exhibited an ultra-small working potential of − 0.040 V (vs. reversible hydrogen electrode (RHE)) for the hydrazine oxidation reaction at 10 mA cm−2 in a 1 M KOH/0.5 M hydrazine solution. The assembled RuCoOx@NC∥RuCoOx@NC membrane-free overall hydrazine splitting electrolyzer only required ultralow cell voltages of 0.063 and 0.505 V to produce 10 and 100 mA cm−2, with remarkable long-term stability, demonstrating its exceptional bifunctional activity. Ex situ Raman spectroscopy results indicate that both Co3O4 and RuO2 species contribute to the electrocatalytic activity of the RuCoOx@NC composite. This work suggests a potential strategy for developing bifunctional electrocatalytic materials for energy-saving hydrogen production to solve future energy demands.

High-efficient sunlight-driven hydrogen production from methanol steam reforming on a novel photo-thermo-catalysis and thermo-catalysis dual-bed reactor

Sunlight-driven methanol-steam-reforming (MSR) reaction using solar energy promises efficient production and safe transportation of hydrogen energy while storing solar energy. However, the low efficiency of photo-reforming and the high cost of thermo-reforming, intrinsically due to limited usage of full-spectrum solar energy, pose a significant challenge to practical application. Here, we propose a sunlight-driven dual-bed photo-thermo-catalytic reactor (DBPTR) for high-efficient hydrogen production from MSR with the cascaded utilization of photo-thermo-catalysis (PTC) over Pt-CuO catalyst bed and thermo-catalysis (TC) over CuO/ZnO/Al2O3 catalyst bed, respectively. The experimental data verify that the overall solar-to-hydrogen (STH) efficiencies of DBPTR remarkably achieve 22.5% in the laboratory and 20.3% outdoors, respectively. These excellent performances are evidently attributed to the fact that our DBPTR could harvest the short-wave radiation (high-energy photons) in the PTC bed for photo-thermo-driven hydrogen production and confine the long-wave radiation (low-energy photons) in the TC bed for thermo-driven hydrogen production. Meanwhile, the proposed DBPTR has been proved to be scaled-up and operate under a reasonably concentrated irradiance of 16 kW m−2 with the above high STH efficiency, harmonizing the high-performance reactor, low-cost concentrator and moderate-accuracy sun-tracker. This work opens up a novel practical pathway towards high-efficient solar-to-chemical conversion.

NH2-MIL-101(Fe)@ZnIn2S4/ZnS heterojunction nanoreactors for efficient photocatalytic-Fenton performance via in-situ H2O2 evolution

NH2-MIL-101(Fe)@ZnIn2S4/ZnS core-shell nanoreactors with S vacancy defects as photocatalytic-Fenton system are fabricated via hydrothermal approach. The introduction of S vacancy in ZnIn2S4 can generate defect levels and thus improve the visible light absorption. The compact core-shell structure formed between ZnIn2S4 and NH2-MIL-101(Fe) provides adequate surface active sites. The short charge transfer path of the formed dual Z-scheme heterojunction nanoreactor greatly accelerates the charge transfer and separation efficiency. It is worth noting that the nanoreactors can produce a large amount of H2O2 and construct an excellent photocatalytic-Fenton system. Under visible light irradiation, NH2-MIL-101(Fe)@ZnIn2S4/ZnS has a high photocatalytic hydrogen production efficiency of 25.371 mmol/g/h and the high degradation efficiency of 99.8% within 150 min for tetracycline. The resultant NH2-MIL-101(Fe)@ZnIn2S4/ZnS photocatalysts will have potential applications in fields of energy and environment.

Mo2C nanocrystalline coupling with Ni encapsulated in N-doped fibrous carbon network as bifunctional catalysts towards advanced anion exchange membrane electrolyzers

Anion exchange membrane water electrolysis (AEMWE) has been considered to be the promising approach for cost-effective hydrogen production. However, the noble metal catalysts of AEM enable it still under the early stage of development. Herein, Mo2C nanocrystalline coupling with Ni have been successfully encapsulated into robust carbonaceous network (Mo2C/NC@0.5Ni) as inexpensive transition metal catalysts for AEM electrolyzers. The Mo2C nanocrystals are uniformly confined in N doped porous carbon network which is derived from the decomposition of PVP and urea during carbonation process. Importantly, rational designed Ni layers are also coated on the surface of the network structure. When utilized as bifunctional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), the Mo2C/NC@ 0.5Ni can achieve desirable overpotentials of 103 mV and 307 mV at a current density of 10 mA cm−2 in 1 M KOH, respectively. Furthermore, the Mo2C/NC@ 0.5Ni‖Mo2C/NC@ 0.5Ni AEM electrolyzers requires only a voltage of 1.9 V to reach a current density of 110.5 mA cm−2 with remarkable durability over 50 h. Numerous interconnected porous structure and defects caused by N doping can provide abundant active sites, facilitate electrons transportations and suppress the aggregation of inner Mo2C. Particularly, the conductive Ni layers could effectively improve the structural strength and induce the synergistic effect with Mo2C component, thereby, improving the catalytic activity and stability. In addition, the DFT calculation results indicate that the Mo2C/NC@ 0.5Ni catalyst has a lower Gibbs free energy of hydrogen adsorption (ΔGH*=−0.21 eV), which is beneficial to its HER catalytic activity. This work provides an insight in developing advanced AEMWE for high efficient and green hydrogen production.

Boosting Water Oxidation on Novel Oxygen Electrode Via Surface Metal Exsolution in Protonic Ceramic Electrochemical Cell

The protonic ceramic electrochemical cell (PCEC) is an emerging and attractive technology that converts energy to hydrogen using solid oxide proton conductors at intermediate temperatures. At this temperature range, the water oxidation reaction (WOR) and oxygen evolution reaction (OER) are dominant for the overall electrode reaction while the development of electrode materials is limited and primarily reply on the knowledge from the conventional oxygen-ion conducting counterpart. Here, we developed a novel Ruddlesden-popper (R-P) electrode that presented excellent electrocatalytic activity and durability, resulted in higher hydrogen production efficiency. The present study could provide a new perspective for materials design and bring more research opportunities in the field.

Structural Reliability Analysis of Large Planar Steam Solid Oxide Electrolysis Cells

Solid oxide electrolysis cells (SOEC) have been receiving significant attention recently because of their high energy efficiency and fast hydrogen production. In our previous study, a multi-physics modeling framework to simulate the SOEC performance and structural reliability of planar SOEC design was developed and demonstrated. The electrochemical reactions, fluid dynamics, species transport, electron transfer, and heat transfer were modeled in the commercial computational fluid dynamics (CFD) software STAR-CCM+. The thermomechanical analysis and the associated structural reliability evaluations were conducted using the commercial finite element analysis software ANSYS. The electrochemistry model was validated by using the experimentally obtained current-voltage (I-V) characteristics of the electrode-supported SOECs. In this study, this framework was applied on a large 300 cm2 steam planar SOEC design, and systematically studied the structural reliability under combinations of cell operating conditions, with cell voltage 1-1.5 V, steam fraction in fuel inlet 0.7-0.9, air inlet flow rate 0-10 L/min, fuel inlet flow rate 2.5-12.5 L/min, and inlet temperature 600-900 C. In the modeling framework, all the cells were investigated under the adiabatic thermal conditions, which is equivalent to packing the cell in an insulated container. This induced the relatively larger temperature variation than in the smaller cell designs. This cell internal temperature non-uniformity may further enhance the spatial variations of open circuit voltage, activation loss, and ionic conductivity in the cell, which all influence the overall cell performance. This situation is more obvious when the cell voltage is higher than 1.35V, under which the cell is significantly heated along the steam flow direction. Traditionally, it is assumed that the cell internal temperature spatial variation plays an important role on cell structural reliability. However, because it was assumed that all the components in cell are stress free at 850 , the cell temperature deviation from 850 is more critical to the stress distribution and structural reliability in the cell. For the investigated cells in the practical conditions, like 750 C inlet temperature and varying voltage from 1.05 to 1.5 V, the highest first principal stress is always in the air side electrode, which is around 45 MPa. This is explained by the higher coefficient of thermal expansion of LSCF-GDC with respect to the other layers. This may indicate that the failure would possibly occur in the air side electrode, but at low risk due to the relatively higher Weibull characteristic strength.