High-efficiency Hydrogen Production Research Articles

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.

Surface treatment of GaN nanowires for enhanced photoelectrochemical water-splitting

High-efficiency hydrogen production through photoelectrochemical (PEC) water splitting has emerged as a promising solution to address current global energy challenges. III-nitride semiconductor photoelectrodes with nanostructures have demonstrated great potential in the near future due to their high light absorption, tunable direct band gap, and strong physicochemical stability. However, several issues, including surface trapping centers, surface Fermi level pinning, and surface band bending, need to be addressed. In this work, enhanced photovoltaic properties have been achieved using gallium nitride (GaN) nanowires (NWs) photoelectrodes by adopting an alkaline solution surface treatment method to reduce the surface states. It was found that surface oxides on NWs can be removed by an alkaline solution treatment without changing the surface morphology through X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and other characterization methods. These findings provide new insights to the development of high-efficiency photoelectrodes for new energy source applications.

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.

Deconvolution of Impedance Spectrums in an Anion Exchange Membrane Electrolyzer with Embedded Voltage Probes

High-efficient hydrogen production requires a minimized electrical work dissipation, which contributed by the resistances of all electrolyzer components during the operation. The electrochemical impedance spectroscopy (EIS) offers the understanding of resistances from different components based on their response to the alternative current frequency. However, the responses are overlapped, and it results in the highly convoluted impedance of the electrodes and limited information of the electrode processes. In this study, voltage probes are embedded in an anion exchange membrane (AEM) electrolyzer, which allow the EIS measurements of individual cell components with a three-electrode or four-electrode approach. Different metal probes made from Pt, Au and Ag are employed to separate the electrolyzer impedance. The summation of the impedances from individual cell components matches well with the total impedance of the entire cell with the error of less than 5%. Therefore, the embedded voltage probes in AEM provides a powerful platform to investigate the kinetics of HER and OER processes separately.

Performance improvement of the liquid-fed SO2-depolarized electrolyzers for anolyte with high H2SO4 concentration

As the hydrogen producing step of the hybrid sulfur process, SO2-depolarized electrolysis (SDE) needs to be operated with anolyte of high H2SO4 concentration, aiming at the high hydrogen production efficiency. However, the SDE cell is facing the challenge of rising impedance when anolyte H2SO4 concentration is increased. In this study, the performance of liquid-fed SDE cells is improved by using a thinner PEM and three-dimensional anode, especially for the anolyte with high H2SO4 concentration. The underlying mechanism of the SDE performance improvement is also discussed. The results show that effectively reducing the concentration polarization impedance is the key to improving the SDE performance. Significantly different from what is expected, PEM thickness reduction could not sharply decrease ohmic impedance. Instead, the application of thin PEMs can significantly reduce the concentration polarization impedance of the cathode reaction. As for the application of three-dimensional anode, it decreases anode concentration polarization dramatically. Finally, the combination of PEM thickness reduction and three-dimensional anode greatly improves the SDE performance of the electrolyzer. The influence of operating conditions on performance is studied for the optimized cell GF-212. When the anolyte H2SO4 concentration set at 50 wt%, the current density could reach 560 mA/cm2 at 1.0 V cell voltage, 360 mL/min anolyte flow rate and 80 °C.

Enhanced metal−promoter interaction over Na modified Co2C nanoprisms for high-efficiency hydrogen production from methanol steam reforming

As an important application for methanol-based energy-storage systems, methanol steam reforming (MSR) using appropriate catalysts can provide clean hydrogen via onboard production for fuel cells. However, owing to their unsatisfactory activity and stability, the use of the most common catalysts, including Cu-based and groups 8–––10 transition metals, remains challenging. Herein, a series of Na-promoted Co2C nanoprism catalysts containing different Na loadings was used for the first time in MSR. The 1Na/Co2C catalyst showed an excellent activity and stability for MSR, with H2 production rates as high as 4637.9 μmol/gcat/min at 250 °C, which outperforms most of the reported catalysts. In-depth characterizations revealed that a strong interaction between Na and Co2C stabilized the catalyst and promoted the dissociation of CH3OH and H2O. A further investigation of the reaction mechanism revealed that the reaction proceeded via the dehydrogenation of methanol and sequential water−gas shift reactions. Density functional theory calculations revealed that the Co2C (101) surface exhibited the lowest energy barrier and that the methoxy dehydrogenation was the rate-determining step. This work provides further valuable insights into the rational design of transition-metal carbide catalysts for MSR.

Coriolus versicolor laccase-based inorganic protein hybrid synthesis for application in biomass saccharification to enhance biological production of hydrogen and ethanol

In this study, a bio-friendly inorganic protein hybrid-based enzyme immobilization system using partially purified Coriolus versicolor laccase (CvLac) was successfully applied to biomass hydrolysis for the enhancement of sugar production aimed at generating biofuels. After four days of incubation, the maximum CvLac production was achieved at 140 U/mg of total protein in the presence of inducers such as copper and wheat bran after four days of incubation. Crude CvLac immobilized through inorganic protein hybrids such as nanoflowers (NFs) using zinc as Zn3(PO4)2/CvLac hybrid NFs (Zn/CvLac-NFs) showed a maximum encapsulation yield of 93.4% and a relative activity of 265% compared to free laccase. The synthesized Zn/CvLac-NFs exhibited significantly improved activity profiles and stability compared to free enzymes. Furthermore, Zn/CvLac-NFs retained a significantly high residual activity of 96.2% after ten reuse cycles. The saccharification of poplar biomass improved ∼2-fold in the presence of Zn/CvLac-NFs, with an 8-fold reduction in total phenolics compared to the control. The Zn/CvLac-NFs treated biomass hydrolysate showed high biological hydrogen (H2) production and ethanol conversion efficiency of up to 2.68 mol/mol of hexose and 79.0% compared to the control values of 1.27 mol of H2/mol of hexose and 58.4%, respectively. The CvLac hybrid NFs are the first time reported for biomass hydrolysis, and a significant enhancement in the production of hydrogen and ethanol was reported. The synthesis of such NFs based on crude forms of diverse enzymes can potentially be extended to a broad range of biotechnological applications.

One-pot synthesized Li, V co-doped Ni3S2 nanorod arrays as a bifunctional electrocatalyst for industrialization-facile hydrogen production via alkaline exchange membrane water electrolysis

The design of a bifunctional electrocatalyst with excellent performance in water electrolysis under high current densities for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with non-noble metals-based catalysts has been challenging. A novel bifunctional electrocatalyst constituted as the lithium and vanadium (Li, V) co-doped nickel sulfide (Ni3S2) nanorod arrays (LVN-0.1) is designed and investigated to take this challenge. The overall water splitting (OWS) electrolyzer constructed with our LVN-0.1 catalyst exhibited low cell voltages of 1.44 and 1.95 V to achieve 10 and 1000 mA/cm2, respectively, with excellent durability, which is almost the best Ni3S2-based electrocatalyst reported to date. The practical scale-up LVN-0.1 stack cell of 2 × 2 cm2 required 1.92 and 2.02 V to achieve high current densities at the industrial level at 500 and 1000 mA/cm2, respectively. Notably, our alkaline stack cell achieved a cell-efficiency of 61.9% and cell stability for 200 h at 1000 mA/cm2, while commercial alkaline cells have kept operating below 500 mA/cm2 to avoid the drop-off of binder-coated electrocatalysts. This study provides a facile way to design bifunctional electrocatalysts for realizing high efficient and stable hydrogen production by alkaline water splitting.

A low-temperature ammonia electrolyser for wastewater treatment and hydrogen production

Ammonia is a pollutant present in wastewater and is also a valuable, carbon-free hydrogen carrier. Stripping, recovery, and anodic oxidation of ammonia to produce hydrogen via electrolysis is gaining momentum as a technology, yet the development of an inexpensive, stable catalytic material is imperative to reduce cost. Here, we report on a new nickel-copper (NiCu) catalyst electrodeposited onto a high surface area nickel felt (NF) as an anode for ammonia electrolysis. Cyclic voltammetry demonstrated that the catalyst/substrate combination reached the highest current density (200 mA cm−2 at 20 °C) achieved for a non-noble metal catalyst. A NiCu/NF electrode was tested in an anion exchange membrane electrolyser for 50 h; it showed good stability and high Faradaic efficiency for ammonia oxidation (88%) and hydrogen production (99%). We demonstrate that this novel electrode catalyst/substrate material combination can oxidise ammonia in a scaled system, and hydrogen can be produced as a valuable by-product at industrial-level current densities and cell voltages lower than that for water electrolysis.

Oxyanion-Coordinated Co-Based Catalysts for Optimized Hydrogen Evolution: The Feedback of Adsorbed Anions to the Catalytic Activity and Mechanism

In order to achieve high-efficiency hydrogen production, researchers always focus on the catalyst itself but rarely consider the feedback of corresponding component spillover and re-adsorption in the catalyst to the reaction activity. This work investigates the promoting effect of vanadium species on the hydrogen evolution reaction (HER) performance of Co3O4. Multiple characterizations indicate that VOx dissolves during the HER and exists in 1.0 M KOH as VO43–. In situ Raman spectroscopy and experimental results show that Co3O4 will be converted to Co(OH)2 and bound to free VO43– through O atoms (Co–O–VO43–), which acts as the active center of HER. More oxygen vacancies (Ov) are also generated on the catalyst surface. The extra addition of VO43– to the electrolyte can not only repair the durability of Co3O4 but also promote the HER activity of Co5.47N, Co3S4, and Co(OH)2. The findings in this work contribute to an in-depth understanding of the structural transition mechanism and activity origin of catalysts under reaction conditions.

Ethylenediamine-assisted solvothermal synthesis of ZnS/ZnO photocatalytic heterojunction for high-efficiency hydrogen production.

Organic-inorganic hybrid materials have emerged as a class of novel materials over the last two decades, as they combine functional organic components and inorganic building blocks into unique materials through various chemical or physical interactions. In the present work, the importance of the use of ethylenediamine in sulfided materials applied to photocatalytic processes in the H2 production is demonstrated. The ZnS/ZnO heterojunction was prepared by the solvothermal synthesis in the presence and absence of ethylenediamine. The photocatalytic behavior showed that the addition of ethylenediamine increases the photocatalytic efficiency up to eight times compared to the photocatalyst without the organic agent. The materials were characterized by X-ray diffraction, scanning electron microscopy, infrared and UV-visible spectroscopies of solids, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, and photoelectrochemical characterization. The ethylenediamine plays a double role: to stabilize the cubic phase of zinc sulfide and to act as a promoter molecule of charge transfer on the surface of ZnS/ZnO/en heterojunction, slowing down the rate of recombination of the electron-hole pair, which is reflected in a decrease in the resistance to transfer of charge carriers, improving the H2 production rate until 1564µmolh-1g-1.