Energy-saving Hydrogen Production Research Articles

Recent Advances and Perspectives on Coupled Water Electrolysis for Energy-Saving Hydrogen Production.

Overall water splitting (OWS) to produce hydrogen has attracted large attention in recent years due to its ecological-friendliness and sustainability. However, the efficiency of OWS has been forced by the sluggish kinetics of the four-electron oxygen evolution reaction (OER). The replacement of OER by alternative electrooxidation of small molecules with more thermodynamically favorable potentials may fundamentally break the limitation and achieve hydrogen production with low energy consumption, which may also be accompanied by the production of more value-added chemicals than oxygen or by electrochemical degradation of pollutants. This review critically assesses the latest discoveries in the coupled electrooxidation of various small molecules with OWS, including alcohols, aldehydes, amides, urea, hydrazine, etc. Emphasis is placed on the corresponding electrocatalyst design and related reaction mechanisms (e.g., dual hydrogenation and N-N bond breaking of hydrazine and C═N bond regulation in urea splitting to inhibit hazardous NCO- and NO- productions, etc.), along with emerging alternative electrooxidation reactions (electrooxidation of tetrazoles, furazans, iodide, quinolines, ascorbic acid, sterol, trimethylamine, etc.). Some new decoupled electrolysis and self-powered systems are also discussed in detail. Finally, the potential challenges and prospects of coupled water electrolysis systems are highlighted to aid future research directions.

A Zero-Gap Electrolyzer Enables Supporting Electrolyte-Free Seawater Splitting for Energy-Saving Hydrogen Production.

Membrane-assisted direct seawater splitting (DSS) technologies are actively studied as a promising route to produce green hydrogen (H2), whereas the indispensable use of supporting electrolytes that help to extract water and provide electrochemically-accelerated reaction media results in a severe energy penalty, consuming up to 12.5 % of energy input when using a typical KOH electrolyte. We bypass this issue by designing a zero-gap electrolyzer configuration based on the integration of cation exchange membrane and bipolar membrane assemblies, which protects stable DSS operation against the precipitates and corrosion in the absence of additional supporting electrolytes. The heterolytic water dissociation function of the bipolar membrane in situ creates an asymmetric acidic-alkaline environment, kinetically facilitating H2 and O2 evolution reactions. When working in natural seawater without any chemical inputs, this zero-gap electrolyzer sustains nearly 100 % Faradaic efficiency toward H2 for 120 h at a current density of 100 mA cm-2. With the high-integrity merit, our electrolyzer can be facilely scaled up into practical cell stacks with significantly increased active area and promising prospects for volume/space-sensitive application scenarios. This electrolyzer concept opens an underexplored design space for energy-saving H2 production from low-grade saline water sources, being complementary to, and potentially competitive with the pre-purification Schemes.

Sustainable and energy-saving hydrogen production via binder-free and in situ electrodeposited Ni-Mn-S nanowires on Ni-Cu 3-D substrates.

Electrochemical water splitting, with its oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), is undoubtedly the most eco-friendly and sustainable method to produce hydrogen. However, water splitting still requires improvement due to the high energy consumption caused by the slow kinetics and large thermodynamic potential requirements of OER. Urea-water electrolysis has become increasingly appealing compared to water-splitting because of the remarkable decline in the cell potential in the hydrogen production process and less energy consumption; it also offers a favorable opportunity to efficiently treat wastewater containing a significant amount of urea. In this work, Ni-Mn-S/Ni-Cu nano-micro array electrocatalysts were synthesized by a two-step and binder-free electrochemical deposition technique and investigated as an effective electrode for the HER and urea oxidation reaction (UOR). According to the electrochemical results, the optimized electrode (Ni-Mn-S/Ni-Cu/10) showed excellent electrocatalytic activity for the HER (64 mV overpotential to achieve the current density of 10 mA cm-2 and Tafel slope of 81 mV dec-1) in alkaline solution. When Ni-Mn-S/Ni-Cu/10 is employed as a UOR anode in an alkaline solution containing urea, it achieves a current density of 10 mA cm-2 at 1.247 V vs. RHE. In addition, when the optimized sample was utilized as a bi-functional electrode for overall urea-water electrolysis (HER-UOR), the cell voltage reached 1.302 V at 10 mA cm-2 (which is 141 mV less than that for HER-OER). The electrocatalytic stability results unequivocally revealed small changes in voltage during a 24 h test and showed good durability. This non-noble metal electrocatalyst, prepared by the electrodeposition synthesis method, is a promising solution to implement low-cost hydrogen production and wastewater treatment.

Vanadium-regulated nickel phosphide nanosheets for electrocatalytic sulfion upgrading and hydrogen production.

The electrochemical sulfion oxidation reaction (SOR) is highly desirable to treat sulfion-rich wastewater and achieve energy-saving hydrogen production when coupled with the cathodic hydrogen evolution reaction (HER). Herein, we propose a thermodynamically favorable SOR to couple with the HER, and develop vanadium-doped nickel phosphide (V-Ni2P) nanosheets for simultaneously achieving energy-efficient hydrogen production and sulfur recovery. V doping can efficiently adjust the electronic structure and improve intrinsic activity of Ni2P, which exhibits outstanding electrocatalytic performances for the HER and SOR with low potentials of -0.093 and 0.313 V to afford 10 mA cm-2. Remarkably, the assembled V-Ni2P-based hybrid water electrolyzer coupling the HER with the SOR requires small cell voltages of 0.389 and 0.834 V at 10 and 300 mA cm-2, lower than those required in a traditional water electrolysis system (1.5 and 1.969 V), realizing low-cost sulfion upgrading to value-added sulfur and hydrogen generation. This work provides an approach for energy-saving hydrogen production and toxic waste degradation.

Highly Dispersed Ni-Fe Active Sites on Fullerene based Electron Buffer to boost Oxygen Evolution Reaction

It is critical to develop highly efficient electrocatalysts for water splitting to achieve energy-saving hydrogen production. Recently, fullerene-based electrocatalysts have been widely reported for cathodic hydrogen evolution reaction (HER), while...

NiMo-based alloy and its sulfides for energy-saving hydrogen production via sulfion oxidation assisted alkaline seawater splitting

NiMo-based alloy and its sulfides for energy-saving hydrogen production via sulfion oxidation assisted alkaline seawater splitting

Novel Selenide Composite as an Effective Bifunctional Electrocatalyst for Energy-Saving Hydrogen Production through Methanol-Assisted Water Electrolysis

Novel Selenide Composite as an Effective Bifunctional Electrocatalyst for Energy-Saving Hydrogen Production through Methanol-Assisted Water Electrolysis

Manipulating Trimetal Catalytic Activities for Efficient Urea Electrooxidation-Coupled Hydrogen Production at Ampere-Level Current Densities.

Replacing the oxygen evolution reaction (OER) with the urea oxidation reaction (UOR) in conjunction with the hydrogen evolution reaction (HER) offers a feasible and environmentally friendly approach for handling urea-rich wastewater and generating energy-saving hydrogen. However, the deactivation and detachment of active sites in powder electrocatalysts reported hitherto present significant challenges to achieving high efficiency and sustainability in energy-saving hydrogen production. Herein, a self-supported bimetallic nickel manganese metal-organic framework (NiMn-MOF) nanosheet and its derived heterostructure composed of NiMn-MOF decorated with ultrafine Pt nanocrystals (PtNC/NiMn-MOF) are rationally designed. By leveraging the synergistic effect of Mn and Ni, along with the strong electronic interaction between NiMn-MOF and PtNC at the interface, the optimized catalysts (NiMn-MOF and PtNC/NiMn-MOF) exhibit substantially reduced potentials of 1.459 and -0.129 V to reach 1000 mA cm-2 during the UOR and HER. Theoretical calculations confirm that Mn-doping and the heterointerface between NiMn-MOF and Pt nanocrystals regulate the d-band center of the catalyst, which in turn enhances electron transfer and facilitates charge redistribution. This manipulation optimizes the adsorption/desorption energies of the reactants and intermediates in both the HER and UOR, thereby significantly reducing the energy barrier of the rate-determining step (RDS) and enhancing the electrocatalytic performance. Furthermore, the urea degradation rates of PtNC/NiMn-MOF (96.1%) and NiMn-MOF (90.3%) are significantly higher than those of Ni-MOF and the most reported advanced catalysts. This work provides valuable insights for designing catalysts applicable to urea-rich wastewater treatment and energy-saving hydrogen production.

In-situ development of highly active Ni-Cu-P@Co-Se as active and stable electrode for energy-saving hydrogen production and urea oxidation reaction

Here, a simple two-step method for synthesizing of unique, active and stable Ni-Cu-P@Co-Se electrocatalyst is introduced. The fabricated electrode demonstrated favorable performance in application as electrocatalyst for hydrogen evolution reaction (HER) processes. When the current density increased from 5 to 10 mA.cm−2, the η10 decreased from 157 to 94 mV which indicated 40 % improvement in catalytic activity. In addition, the deposited electrode at 10 mA.cm−2 demonstrated best UOR performance which needed only 1.323 V vs RHE at 10 mA.cm−2, due to having high electrochemical active area, interfacial engineering, and the optimized interaction between the electrode and the electrolyte. When the Ni-Cu-P@Co-Se electrode was used as a bi-functional electrode in the urea electrolysis process, the cell potential value was 1.413 V. The synthesized electrode presented slight changes in overpotential during stability test. This work introduces an economical and effective method for the synthesis of active electrodes in energy-saving hydrogen production systems.

A 2D/3D hierarchical hybrid enables energy-saving hydrogen production coupled with glycerol and urea electro-oxidation

The design and development of high-performance electrocatalysts is crucial to improve the utility of anodic reaction for energy-saving hydrogen production. Herein, we present a novel catalyst with 2D/3D multistage structure for the electro-oxidation of renewable biomass and harmful waste to assist hydrogen generation. The hierarchical configuration of NiO/CoO nanosheets interconnected by hollow carbon spheres, leveraging both 2D and 3D advantages. This structure provides rich surface and edge active sites as well as affluent electron and mass transfer pathways, resulting in the accelerated dynamics of electro-oxidation. The hollow carbon spheres serve as a buffering agent to alleviate the strain caused by repetitive redox reactions during electrolysis, thereby bestowing exceptional structural and chemical stability for prolonged operational durability. Additionally, the multiple continuous hetero-interfaces between NiO and CoO, NiO and carbon as well as CoO and carbon can ensure the fast electron transport, leading to the expedited reaction kinetics with the synergistic effect of phase engineering between NiO, CoO and carbon shell. As a result, the 3D carbon shells jointed 2D NiO/CoO hybrids demonstrate promising catalytic activities on electro-oxidation for energy-efficient hydrogen production (∼100 %FE) coupled with urea oxidation and formic acid synthesis with excellent selectivity (95.40 %) and satisfied faradic efficiency (91.6 %).

Heteroatom Engineering in Earth-Abundant Cobalt Electrocatalyst for Energy-Saving Hydrogen Evolution Coupling with Urea Oxidation.

The development of multifunctional electrocatalysts with high performance for electrocatalyzing urea oxidation-assisted water splitting is of great significance for energy-saving hydrogen production. In this work, we demonstrate a novel heteroatom engineering strategy for development of B-doped Co as a multifunctional electrocatalyst for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and urea oxidation reaction (UOR). Density functional theory (DFT) results suggest that a B dopant can efficiently adjust the electron reconstruction of the exposure of Co sites nearby and facilitate electron transfer, resulting in an optimal d-band center along with a lower Gibbs free energy barrier. Ultimately, the obtained B-Co exhibits pH-universal HER properties in various electrolytes. A highly efficient HER performance with overpotentials as low as 27, 163, and 430 mV to -10, -100, and -500 mA cm-2 in 1.0 M KOH, respectively, is observed for the B-Co electrode. More importantly, the UOR-assisted electrolyzer only requires a voltage input of 1.55 V to produce the current densities of 50 mA cm-2, resulting in a 200 mV saving-energy potential compared to water electrolysis, demonstrating its high efficiency of hydrogen production in industrial applications.

Al-etching-induced defect engineering in NiAl LDHs for promoting multifunctional electrocatalytic oxidations: Water oxidation and urea oxidation

Electrocatalytic water splitting is a promising avenue to produce green hydrogen for future sustainable development. Developing multifunctional catalysts with high-performance toward urea oxidation reaction (UOR) and oxygen evolution reaction (OER) offers a unique approach for simultaneously achieving the degradation of urea-containing wastewater and energy-saving hydrogen production. Ni-based materials are a kind of promising materials for electrocatalysis, since its abundant reserve and tolerance. However, low intrinsic activity and catalytic efficiency hinder its wide application. Here, a defect engineering strategy is developed to create vacancies on NiAl layer double hydroxides (LDHs) catalysts by selectively etching Al ions in strong alkaline solution. The obtained NiAl LDHs with rich defects (D-NiAl LDHs) exhibit good OER performance with overpotential of 264 mV to achieve a current density of 10 mA cm−2 and a Tafel slope of 39.8 mV dec−1. In addition, the D-NiAl LDHs catalysts also show excellent UOR activity using a potential of 1.328 V vs. RHE @ 10 mA cm−2 in alkaline solution. In comparation to NiAl LDHs, the enhanced performance of D-NiAl LDHs toward oxidation of small-molecule OH− and urea could be attributed to electronic regulation of defects and a larger electrochemical surface area. Partially replacing the OER with the UOR, the driving voltage of overall water splitting reduces effectively from 1.856 V to 1.688 V at a current of 100 mA cm−2.

Natural DNA-derived ultrafine Ir/Ir2P hybrid on porous N, P-codoped carbon for pH-universal energy-saving hydrogen production assisted by electrocatalytic hydrazine oxidation

Due to the intrinsic slow kinetics and high potential of the anodic oxygen evolution reaction (OER), hydrazine oxidation reaction (HzOR) with ultralow potential is a viable substitute to combine the cathodic hydrogen evolution reaction (HER) for the energy-saving hydrogen generation. Therefore, it is a compelling demand to explore high-performance electrocatalysts for bifunctional HER and HzOR. Herein, natural DNA was employed to prepare the uniform and ultrafine Ir/Ir2P hybrids loaded on N, P-codoped porous carbon (Ir/PNPC) through a facile “mix-and-pyrolyze” approach. Benefitting from abundant heteroatom doping, large surface area and high degree of graphitization, Ir/PNPC only requires the ultrasmall potentials of −22/-347/-54 mV at 100 mA cm−2 for HER, 46/172/227 mV at 10 mA cm−2 for HzOR, and 167/836/864 mV at 100 mA cm−2 for the constructed two-electrode overall hydrazine splitting (OHzS) in the alkaline, neutral and acidic electrolytes, respectively, all exceeding Pt/C and also showing the remarkable energy-efficient superiority over the conventional water splitting. Furthermore, the OHzS system can be readily driven by the as-prepared direct N2H4/H2O2 fuel cell and commercial solar cell with decent H2 generation rate of 1.245 and 1.392 mmol h−1, respectively. This study provides lights on the preparation of the advanced pH-universal HER and HzOR bifunctional electrocatalysts by natural DNA and is also encouraging for the energy-saving H2 production.

Theoretical design and synthesis of Co30Ni60/CC for high selective methanol oxidation assisted energy-saving hydrogen production

The integration of methanol oxidation reaction (MOR) with hydrogen evolution reaction (HER) represents an advanced approach to hydrogen production technology. Nonetheless, the rational design and synthesis of bifunctional catalysts for both MOR and HER with exceptional activity, stability and selectivity present formidable challenges. In this work, firstly, density functional theory (DFT) was utilized to design and evaluate material models with high performance for both MOR and HER. Secondly, guided by DFT, Co30Ni60/CC (CC, carbon cloth) composites with a leaf-like nanosheet structure were successfully fabricated via electrodeposition. In the MOR process, Ni acts as the predominant active center, while Co amplifies the electrochemically active surface area (ECSA) and enhances the selectivity of methanol oxidation. Conversely, in the HER process, Co serves as the primary active center, with Ni augmenting the charge transfer rate. The electrochemical results demonstrate that Co30Ni60/CC exhibits exceptional performance in both MOR and HER at a current density (j) of 10 mA cm−2, with peak potentials of 1.323 V and −95 mV, respectively. Additionally, it shows remarkable selectivity for the oxidiation of methanol to high value-added formic acid. Thirdly, following a 100 h chronopotentiometry (CP) test, the required potential demonstrates an increase of 4.9 % (MOR) and 8.1 % (HER), signifying the superior stability of Co30Ni60/CC compared to those reported in the literature. The exceptional performance of Co30Ni60/CC can be primarily attributed to that the leaf-like nanosheets structure not only exposes a plethora of active sites but also facilitates electrolyte diffusion, the monolithic structure prepared by electrodeposition enhances its stability, and the transfer of electrons from Co to Ni regulates its electronic structure, as corroborated by X-ray photoelectron spectroscopy (XPS) and density of states (DOS) analyses. Finally, at the same j, the voltage required by the Co30Ni60/CC||Co30Ni60/CC electrolytic cell, powered by an electrochemical workstation, is 198 mV lower than that required for alkaline water-splitting. Meanwhile, at higher j (100 mA cm−2), the electrolytic cell exhibits sustained and stable operation for 150 h, enabling high-efficiency hydrogen production and the synthesis of high value-added formic acid.

Nickel-copper alloying arrays realizing efficient co-electrosynthesis of adipic acid and hydrogen

Constructing electrocatalytic overall reaction technology to couple the electrosynthesis of adipic acid with energy-saving hydrogen production is of significant for sustainable energy systems. However, the development of highly-active bifunctional electrocatalysts remains a challenge. Herein, 3D hierarchical nickel-copper alloying arrays with dendritic morphology are manufactured by a simple electrodeposition process, standing for the excellent bifunctional electrocatalyst towards the co-production of adipic acid and H2 from cyclohexanone and water. The membrane-free flow electrolyzer of Cu0.81Ni0.19/NF shows the superior electrooxidation performance of ketone-alcohol (KA) oil with high faradaic efficiencies of over 90% for adipic acid and H2, robust stability over 200 h as well as a high yield of 0.6 mmol h−1 for adipic acid at 100 mA cm−2. In-situ spectroscopy indicates the Cu0.81Ni0.19 alloy contributes to forming more active NiOOH species to involve in the conversion of cyclohexanone to adipic acid, while the proposed reaction pathway undergoes the 2-hydroxycyclohexanone and 2,7-oxepanedione intermediates. Moreover, the theoretical calculations confirm that the optimal electronic interaction, boosted reaction kinetics as well as improved adsorption free energy of reaction intermediates, synergistically endows Cu0.81Ni0.19 alloy with superior bifunctional performance.

Key strategies and future perspectives of anodizing-assisted energy-saving hydrogen production

Key strategies and future perspectives of anodizing-assisted energy-saving hydrogen production

Electrooxidation of glycerol to formic acid coupled with Energy-Saving hydrogen production over ruthenium doped Cobalt-Based nanosheet arrays

The utilization of small molecule oxidation reactions as a substitute for the sluggish oxygen evolution reaction (OER) in traditional water electrolysis represents an innovative approach to achieve efficient hydrogen production while concurrently generating value-added chemicals. Herein, we report an energy-saving H2 production system utilizing electrooxidation of glycerol to generate valuable formate. Cobalt–ruthenium oxide nanosheet arrays (CoRuO/CF) and cobalt–ruthenium bimetallic nanoparticles wrapped by nitrogen-doped carbon nanosheet arrays (CoRuCN/CF) were synthesized for glycerol oxidation reaction (GOR) and hydrogen evolution reaction (HER), respectively, using Co-ZIF nanosheets precursor material supported on copper foam (Co-ZIF/CF) as the substrate. Remarkably, the hybrid electrolysis system can achieve a current density of 10 mA cm−2 with only 1.19 V, which is significantly lower than that required by traditional water-splitting systems. This work demonstrates the promising potential of efficiently utilizing biomass energy and achieving a sustainable production process for fine chemical products.

Modulating Silver Performance in Electrocatalytic Oxidation of HCHO via SMSI between Ag-Co3O4 Interfaces.

The replacement of oxygen evolution reactions with organic molecule oxidation reactions to enable energy-efficient hydrogen production has been a subject of interest. However, further reducing reaction energy consumption and releasing hydrogen from organic molecules continue to pose significant challenges. Herein, a strategy is proposed to produce hydrogen and formic acid from formaldehyde using Ag/Co3O4 interface catalysts at the anode. The key to improving the performance of Ag-based catalysts for formaldehyde oxidation lies in the strong SMSI achieved through the well-designed "spontaneous redox reaction" between Ag and Co3O4 precursors. Nano-sized Ag particles are uniformly dispersed on Co3O4 nanosheets, and electron-deficient Agδ+ are formed by the SMSI between Ag and Co3O4. Ag/Co3O4 demonstrates exceptional formaldehyde oxidation activity at low potentials of 0.32V versus RHE and 0.65V versus RHE, achieving current densities of 10 and 100mA cm-2, respectively. The electrolyzer "Ag/Co3O4||20% Pt/C" achieves over 195% hydrogen efficiency and over 98% formic acid selectivity, maintaining stable operation for 60 hours. This work not only presents a novel approach to precisely modulate Ag particle size and interface electronic structure via SMSI, but also provides a promising approach to efficient and energy-saving hydrogen production and the transformation of harmful formaldehyde.

Simultaneously Boosting Direct and Indirect Urea Oxidation of Nickel Hydroxide via Strategic Yttrium Doping.

Urea electrolysis can address pressing environmental concerns caused by urea-containing wastewater while realizing energy-saving hydrogen production. Highly efficient and affordable electrocatalysts are indispensable for realizing the great potential of this emerging technology. Among the numerous candidates, α-Ni(OH)2 has the merits of good electrocatalytic activity, adjustable heteroelement doping, and low cost; consequently, it has received tremendous attention in the electrolytic fields. Herein, a Y3+-doping strategy is developed to effectively enhance the catalytic performance of nickel hydroxide in the urea oxidation reaction (UOR). Our results show that Y3+ incorporation successfully modulates the electronic structure of α-Ni(OH)2 by inducing Ni3+ formation in the crystal lattice to initiate direct UOR, facilitates the Ni3+/Ni2+ redox transition with higher current responses to promote indirect UOR, and maintains the structural stability of YNi-10 (Ni2+/Y3+ molar ratio = 1:0.1) during long-term UOR operation. Owing to these features, the obtained YNi-10 sample exhibits a higher current density (127 vs 79 mA cm-2 at 1.5 V), a lower Tafel slope (48 vs 75 mV dec-1), a larger potential difference between the UOR and oxygen evolution reaction (OER, 0.26 vs 0.22 V at 80 mA cm-2), a higher reaction rate constant (1.1 × 105 vs 3.1 × 103 cm3 mol-1 s-1), and a reduced activation energy of UOR (2.9 vs 14.8 kJ mol-1) compared with the Y-free counterpart (YNi-0). This study presents a promising strategy to simultaneously boost direct and indirect UORs, providing new insights for further developing high-performance electrocatalysts.

Amorphous-Crystalline Interfaces Coupling of CrS/CoS2 Few-Layer Heterojunction with Optimized Crystallinity Boosted for Water-Splitting and Methanol-Assisted Energy-Saving Hydrogen Production

Amorphous-Crystalline Interfaces Coupling of CrS/CoS2 Few-Layer Heterojunction with Optimized Crystallinity Boosted for Water-Splitting and Methanol-Assisted Energy-Saving Hydrogen Production