Energy-efficient Hydrogen Production Research Articles

Less-Energy Consumed Hydrogen Evolution Coupled with Electrocatalytic Removal of Ethanolamine Pollutant in Saline Water over Ni@Ni3 S2 /CNT Nano-Heterostructured Electrocatalysts.

Energy crises, environmental pollution, and freshwater deficiency are critical issues on the planet. Electrolytic hydrogen generation from saline water, particularly from salt-contained hazardous wastewater, is significant to both environment and energy concerns but still challenging due to the high energy cost, severe corrosion, and the absence of competent electrocatalysts. Herein, a novel strategy is proposed for energy-efficient hydrogen production coupled with electro-oxidation removal of ethanolamine pollutant in saline water. To achieve this, an active and durable heterostructured electrocatalyst is developed by in situ growing Ni@Ni3 S2 core@shell nanoparticles in cross-linked 3D carbon nanotubes' (CNTs) network, achieving high dispersibility and metallic property, low packing density, and enriched exposed active sites to facilitate fast electron/mass diffusion. The unique Ni@Ni3 S2 /CNTs nano-heterostructures are competent for long-term stably electro-oxidizing environmental-unfriendly ethanolamine at a high current density of 100mA cm-2 in saline water, which not only suppresses oxygen and chloride evolution reactions but also decreases the energy consumption to boost hydrogen production. Associated with experimental results, density functional theory studies indicate that the collaborative adsorption of electrolyte ions and ethanolamine molecules can synergistically modulate the adsorption/desorption properties of catalytic active centers on Ni@Ni3 S2 /CNTs surface, leading to long-term stabilized electrocatalysis for efficient ethanolamine oxidation removal and less-energy hydrogen simultaneous production in saline water.

Structural and Componential Engineering of Co2P&CoP@N-C Nanoarrays for Energy-Efficient Hydrogen Production from Water Electrolysis.

The development of electrocatalysts for efficient water splitting is a pivotal and challenging task. Transition-metal phosphides (TMPs) have been known as one of the most promising candidates for the efficient hydrogen evolution reaction (HER) due to their favorable intrinsic reactivity. However, structural engineering related to the gas bubbles evolution and tiny regulation of components concerned with the electronic structure remained as a significant challenge that requires further optimization. Herein, the nanoarrays (NAs) composed of ultrasmall Co2P and CoP nanoparticle-embedded N-doped carbon matrix (Co2P&CoP@N-C) are prepared and demonstrated an overpotential of 62.8 ± 4.7 mV at 10 mA cm-2 in 1.0 M KOH. The nanoarray-structured electrocatalyst revealed the superaerophobicity and facilitates the detachment of the in situ formed hydrogen gas bubbles, ensuring abundant catalytic sites and electrode-electrolyte interface for the mass transfer process. The amount of P doping modulated the local electron density around Co and P atoms, which attains a favorable compromise to afford sufficient electrons for the electrocatalysis and inhibit the negative influence of H2 desorption. Significantly, the lowered overpotential induced by the electrocatalyst surface architecture is much stronger than that of the component content and promotes the electrocatalytic activity.

Integrating electrocatalytic hydrogen generation with selective oxidation of glycerol to formate over bifunctional nitrogen-doped carbon coated nickel-molybdenum-nitrogen nanowire arrays

Achieving energy-efficient hydrogen production via hybrid water electrolysis systems requires not only a well-chosen alternative anodic reaction to replace the sluggish oxygen evolution reaction, but also highly efficient electrocatalysts. Herein, N-doped carbon coated Ni-Mo-N nanowire arrays supported on a nickel foam substrate (NC/Ni-Mo-N/NF) are constructed as a bifunctional electrocatalyst to facilitate electrocatalytic hydrogen production and selectively oxidize glycerol to formate simultaneously. With the desirable structural and compositional advantages of modified surface properties, optimized electronic structure, and Ni/Ni0.2Mo0.8N interfacial synergy effect, the resultant self-supported NC/Ni-Mo-N/NF electrode displays excellent electrocatalytic performance for both the hydrogen evolution reaction and glycerol oxidation reaction in alkaline conditions. Remarkably, the NC/Ni-Mo-N/NF||NC/Ni-Mo-N/NF two-electrode system needs only a cell voltage of 1.38 V at 10 mA cm−2 in 1 M KOH containing 0.1 M glycerol, much lower than that of conventional overall water splitting system (1.57 V at 10 mA cm−2).

Nonprecious bimetallic NiFe ‐layered hydroxide nanosheets as a catalyst for highly efficient electrochemical water splitting

It has become highly necessary to advance stable, cost-effective, and energy-efficient hydrogen production using non-precious metal-based water electrolysis to replace the increasing demand for fossil fuels and maintain environmental safety. Herein, we present the synthesis of non-precious bimetallic Ni1-xFex-layered hydroxide nanosheet films by using a chemical-bath deposition technique for use as oxygen evolution reaction (OER) catalysts for electrochemical water electrolysis. Remarkably, the optimized Ni0.50Fe0.50-layered hydroxide electrode exhibited excellent OER activity in 1 M potassium hydroxide electrolyte while having a low overpotential of 239.7 mV at a current density of 10 mA cm−2 with a small Tafel slope of 38.02 mV dec−1. It was electrochemically stable over 100 hours of continuous OER operation, thereby showing its excellent electrochemical stability. The results from a post-OER study reveal that catalytically active OER sites are associated with the formation of a nickel oxyhydroxide intermediate on the surface of the electrode. The maximum synergy among good electronic conductivity, high diffusion coefficient, and enlarged electrochemically active sites was obtained by optimizing the Ni/Fe ratio and thereby, the OER activity.

Premagnetized Carbon-Catalyst Interface Delivering 650% Enhancement in Electrocatalytic Kinetics of Hydrogen Evolution Reaction

Manipulating heterogeneous electrified interfaces with an external magnetic field (Hₑₓₜ) explicitly mandates the constant presence of Hₑₓₜ for achieving magnetoelectrocatalytic kinetic enhancements. Here, we demonstrate the highest kinetic enhancement of 650% in electrocatalytic hydrogen evolution reaction (HER), without the mandatory presence of Hₑₓₜ. A synergistic interface created in nanostructured hard carbon florets (NCF) decorated with ferro–paramagnetic nanoparticles (Co₃O₄, Co, and Ni–Co) is demonstrated to be critical for both (a) prominent enhancement in HER-kinetics when Hₑₓₜ = 200 mT and (b) sustaining the rapid HER when Hₑₓₜ = 0 mT. Significant lowering of magnetoresistance (22%) and magnetocharge-transfer resistance (84.8%) using a weak Hₑₓₜ = 100 mT leads to a 2.5-fold volumetric increment in hydrogen generation driven by 7% enhancement in electrokinetic activity. Furthermore, all such enhancements are strongly correlated with the magnetic coercivity of the catalyst, implying the role of interfacial mechanistic modulation of the HER by Hₑₓₜ. Additionally, microscopic dimensional enlargement of the structurally flexible NCF promotes such a long-term effect leading to larger magnetocurrent as compared to other carbon-based supports. Our work demonstrates the importance of spin polarization in magnetically active electrocatalytic interfaces and thereby offers a general practical strategy for energy-efficient hydrogen production.

Superhydrophilic Ni-based Multicomponent Nanorod-Confined-Nanoflake Array Electrode Achieves Waste-Battery-Driven Hydrogen Evolution and Hydrazine Oxidation.

The low thermodynamic potential (-0.33V) and safe by-product of N2 /H2 O, make utilizing hydrazine oxidation reaction (HzOR) to replace thermodynamically-unfavorable and kinetically-sluggishoxygen evolution reaction a promising tactic for energy-efficient hydrogen production. However, the complexity of bifunctionality increases difficulties for effective material design, thus hindering the large-scale hydrogen generation. Herein, we present the rationally designed synthesis of superhydrophilic Ni-based multicomponent arrays (Ni NCNAs) composed of 1D nanorod-confined-nanoflakes (2D), which only needs -26mV of working potential and 47mV of overpotential to reach 10mA cm-2 for HzOR and HER, respectively. Impressively, this Ni NCNA electrode exhibits the top-level bifunctional activity for overall hydrazine splitting (OHzS) with an ultralow voltage of 23mV at 10mA cm-2 and a record-high current density of 892mA cm-2 at just 0.485V, also achieves the high-speed hydrogen yield driven by a waste AAA battery for OHzS.

Vanadium-doped hierarchical Cu2S nanowall arrays assembled by nanowires on copper foam as an efficient electrocatalyst for hydrogen evolution reaction

A novel hierarchical vanadium-doped Cu2S nanowall arrays assembled by nanowires (V-Cu2S-Nanowires NW) on copper foam is synthesized by a facile one-step solvothermal method. Interestingly, the nanoparticles furtherly constitute the smallest unit of nanowires. Owing to the unique hierarchical structure with offering plentiful electronics/ions transport pathways and fully exposing catalytic active sites as well as optimizing hydrogen adsorption free energy due to vanadium doped effect, the V-Cu2S-Nanowires NW demonstrates enhanced electrocatalytic activity towards hydrogen evolution reaction (HER) with a low loverpotential of 188 mV to drive 10 mA cm−2 and good durability for at least 20 h. This work provides an effective strategy for rational design of nanostructured Cu-based materials and enhanced energy-efficient hydrogen production.

Porous and amorphous cobalt hydroxysulfide core–shell nanoneedles on Ti-mesh as a bifunctional electrocatalyst for energy-efficient hydrogen production via urea electrolysis

Porous and amorphous CoSx(OH)y core–shell nanoneedles covered by numerous ultra-thin small nanosheets are synthesized successfully on Ti-mesh, and act as a high activity and stability bifunctional catalyst for urea electrolysis.

Bifunctional single-atomic Mn sites for energy-efficient hydrogen production.

The electrocatalytic hydrogen evolution reaction (HER) for H2 production is essential for future renewable and clean energy technology. Screening energy-saving, low-cost, and highly active catalysts efficiently, however, is still a grand challenge due to the sluggish kinetics of the oxygen evolution reaction (OER) in electrolyzing water. Herein, we present a single atomic Mn site anchored on a boron nitrogen co-doped carbon nanotube array (Mn-SA/BNC), which is perfectly combined with the hydrazine electrooxidation reaction (HzOR) boosted water electrolysis concept. The obtained catalyst achieves 51 mV overpotential at the current density of -10 mA cm-2 for the cathodic HER and 132 mV versus the reversible hydrogen electrode for HzOR, respectively. Besides, in a two-electrode overall hydrazine splitting (OHzS) system, the Mn-SA/BNC catalyst only needs a cell voltage of only 0.41 V to output 10 mA cm-1, with strong durability and nearly 100% faradaic efficiency for H2 production. This work highlights a low-cost and high-efficiency energy-saving H2 production pathway.

Hybrid water electrolysis: Replacing oxygen evolution reaction for energy-efficient hydrogen production and beyond

Renewable energy-driven hydrogen generation from water electrolysis has been widely recognized as a promising approach to utilize sustainable energy resources, reduce our dependence on legacy fossil fuels and alleviate net carbon dioxide emissions. However, conventional water electrolyzers suffer from the high overpotentials, mainly due to the sluggish kinetics of anodic oxygen evolution reaction (OER). This reaction also generates reactive oxygen species that could degrade the proton exchange membrane and oxygen that may mix with the cathodic hydrogen to form explosive gaseous mixtures. To address these issues, an innovative hybrid water electrolysis strategy which involves a certain alternative oxidation reaction to replace OER has been developed, and has led to a burgeoning area that sparks much research interest in finding available alternative reactions and their corresponding electrocatalysts. Herein, we summarize the alternative reactions into three groups: (1) the reagent-sacrificing type that can generate H2 with an ultra-low potential while the substrates are oxidized to valueless products; (2) the pollutant-degrading type at which environmental pollutants are used as substrates; (3) the value-added type that produces valuable products at the anode. Catalyst and electrolyzer designs for hybrid electrolysis are also briefly discussed, with an emphasis on the catalyst reconstruction phenomenon. Finally, the present challenges and perspectives are put forward.

Numerical study of sorption-enhanced methane steam reforming over Ni/Al2O3 catalyst in a fixed-bed reactor

The present work deals with the Sorption-Enhanced Methane Steam Reforming (SE-MSR), an interesting and energy-efficient hydrogen production route with in situ CO2 capture. A computational fluid dynamics (CFD) model for an industrial-scale fixed-bed reactor, with Ni/Al2O3 as catalyst and CaO as an adsorbent for CO2 capture, is developed taken into consideration also the coke deposition. Temperature is shown to be the key parameter of the SE-MSR chemical process at large scales. H2 production is constant and maximum until the saturation of CaO sorbent occurs, after which the concentrations of all the other compounds start to vary, and the efficiency of the process begins to drop. When the exothermic carbonation reaction stops, an alteration of the thermal regimes is observed. The absence of the contribution of the exothermic carbonation reaction results in a decrease of the temperature, which in turn determines a lower conversion of CH4 and H2O, according to the endothermic reforming reactions.The maximum H2 outlet mole fraction (dry basis) is 0.8, and it occurs in the presence of CO2 sorption; the value drops to 0.42 once the adsorbent reaches its maximum conversion degree. The molar selectivity in hydrogen relative to the quantity of CH4 fed to the reactor is of the order of 1.75 (with CO2-capture) and 0.8 (without CO2 capture).The molar fluxes obtained and the kinetics of the system model show the excellent choice of the operating conditions of the catalyst to produce a large quantity of hydrogen as well as of the adsorbent, which eliminates the CO2 responsible of coke deposition.

Boosting the oxygen evolution activity of copper foam containing trace Ni by intentionally supplementing Fe and forming nanowires in anodization

Oxygen evolution reaction (OER) is the bottleneck for realizing energy-efficient hydrogen production through water electrolysis in both acid and alkali. Alkaline OER electrocatalyzed by Ni and Co hydroxides are well known which showed unexpected enhancement with the addition of Fe. We found that the commercially procured Cu foam containing trace amount of Ni (~1.5 wt.%) upon anodization formed Cu(OH)2CuO nanowires with conceivable formation of Ni(OH)2 and experienced a notable enhancement in its OER activity. When sufficient amount of Fe was intentionally supplemented during anodization, OER activity of the same was further improved. Specifically, as a combined result of anodization in KOH and in Fe supplemented KOH, overpotential at 50 mA cm−2 was lowered by 153 mV. Such an activation also improved the kinetics of OER by lowering the Tafel slope by 100 mV dec−1. With these, it has been shown here that a moderately active OER catalyst i.e., Cu(OH)2CuO/Cu formed upon the anodization of Cu foam can be turned into a highly active catalyst just by utilizing the trace Ni that it already contains and intentionally supplementing sufficient amount of Fe.

Energy-efficient hydrogen production over a high-performance bifunctional NiMo-based nanorods electrode

Electrochemical water splitting to hydrogen fuel is highly desirable yet challenging mainly limited by sluggish cathodic oxygen evolution reaction (OER). Urea electrolysis can produce hydrogen more energy-savingly by replacing OER process with urea oxidation reaction (UOR) due to favorable thermodynamic potential, however lacking efficient UOR catalysts restricts the industrial application. Here we reported novel NiMo-based nanorods, Ni/Ni0.2Mo0.8N/MoO3, by thermal ammonolysis of NiMo-based precursor as excellent catalyst for OER and hydrogen evolution reaction (HER) with small overpotentials of 252 mV, and 103 mV to achieve a current density of 10 mA cm−2 in 1.0 M KOH. Moreover, the Ni/Ni0.2Mo0.8N/MoO3 shows fabulous catalytic UOR activity with a low potential of 1.349 V at 10 mA cm−2, outperforming most recently reported non-noble metal catalysts and commercial RuO2. More importantly, the cell voltage of urea electrolysis using Ni/Ni0.2Mo0.8N/MoO3 as cathode for HER and anode for UOR is significantly reduced from 1.52 V of traditional water electrolysis to 1.356 V to deliver 10 mA cm−2 with excellent stability for over 400 h, superior to almost recently reported catalysts. The high performances result from the synergistic effect between highly active and conductive metal nickel and nitride, and nanorods arrays grown on 3D substrate. This work demonstrates that this material holds encouraging potential in large-scale energy-saving H2 production and urea-related wastewater treatment.

Pulsed electrodeposition of well-ordered nanoporous Cu-doped Ni arrays promotes high-efficiency overall hydrazine splitting

Bifunctional double-hierarchy porous structured copper-doped nickel cubic nanopores electrocatalyst via a facile two-step pulse electrodeposition-dealloying strategy enable energy-efficient hydrogen production via Overall Hydrazine Splitting.

Efficient hydrogen production via urea electrolysis with cobalt doped nickel hydroxide-riched hybrid films: Cobalt doping effect and mechanism aspect

The exploration of earth-abundant catalysts that are highly active and robustly stable for urea electrooxidation is critical for energy-efficient hydrogen production associated with urea-rich wastewater purification. Herein, Co-doped α-Ni(OH)2 hybrid films with unique ultrafine nanoparticles assembled network structure are constructed as efficient bifunctional electrocatalysts for urea-assisted water electrolysis. By employing a facile potentiodynamic deposition route carried out in a deep eutectic solvent (Ethaline), ultrafine Ni-based nanoparticles with a α-Ni(OH)2 rich surface doping by Co are in-situ grown on Cu foam substrate (Cox-Ni(OH)2 NPs/CF), creating an integrated electrode full of intimate contact interfaces. The doping of Co triggers a structural transition with electronic structure changes at the electrode surface and lowers the onset potential required for Ni(OH)2/NiOOH, which strongly enhances the urea electrolysis activity. Through potential conditioning procedure, the optimized Co0.26-Ni(OH)2 NPs/CF catalyst (with a Ni/Co proportion of 1:0.26) manifests excellent electrocatalytic performance for urea electrolysis in 1.0 M KOH with 0.5 M urea, presenting a low onset potential of 1.27 V vs. RHE for urea oxidation and an overpotential of 106 mV for the hydrogen evolution reaction at 10 mA cm−2. Impressively, the constructed alkaline urea electrolyzer based on Co0.26-Ni(OH)2 NPs/CF delivers 10 mA cm−2at a stable output voltage of 1.42 V with robust durability over 38 h and high selectivity.

Activating Layered Double Hydroxide with Multivacancies by Memory Effect for Energy-Efficient Hydrogen Production at Neutral pH

Sustainable water-splitting hydrogen production has long been considered one of the most promising energy conversion technologies, but enormous challenges remain: for instance, water electrolysis suffers from high overpotential and over energy consumption under neutral pH conditions. Here, taking advantage of the memory effect of layered double hydroxide (LDH), we report an energy-efficient neutral water electrolyzer material based on LDH with multiple vacancy defects. Benefiting from the improved electrical conductivity, larger electrochemical surface area (ECSA), and faster charge transfer, the NiFe LDH with O, Ni, and Fe vacancies exhibits a low overpotential of 87 mV at 10 mA/cm2 for hydrogen evolution reaction (HER) in a pH 7 buffer electrolyte. Impressively, the as-fabricated vacancy-containing NiFe LDH (v-NiFe LDH) splits water with a current density of 10 mA/cm2 at ∼1.60 V in a two-electrode device, outperforming most other water-splitting catalysts in neutral media. Such an electrolyzer setup cou...

Ni-foam supported Co(OH)F and Co–P nanoarrays for energy-efficient hydrogen production via urea electrolysis

Ni-foam-supported Co(OH)F and Co–P nanoarrays were developed for energy-efficient hydrogen production with the assistance of urea electrolysis.

Self-Assembly-Induced Mosslike Fe2O3 and FeP on Electro-oxidized Carbon Paper for Low-Voltage-Driven Hydrogen Production Plus Hydrazine Degradation

Energy-saving electrolytic hydrogen production is the precondition for implementing large-scale hydrogen energy exploitation. Replacing the sluggish water oxidation reaction with thermodynamically more favorable pollutant electro-oxidation (degradation) is a very promising approach to combine energy-efficient hydrogen production and sewage treatment. Herein, a homologous asymmetrical two-electrode configuration, made up of self-assembly induced mosslike Fe2O3 and FeP on electro-oxidized carbon paper (ECP), was used to electrolyze the integrated hydrazine oxidation–hydrogen evolution system. The free-standing Fe2O3/ECP electrode was fabricated by pyrolyzing iron phthalocyanine/ECP self-assembly in air and serves as an anodic reaction catalyst. Subsequent phosphidation of the Fe2O3/ECP leads to the formation of the FeP/ECP catalyst for hydrogen evolution reaction. The cross-linked mosslike Fe2O3 and FeP nanoparticles densely covered on the surface of ECP provide richly exposed catalytic sites and the well-d...

Anodic Hydrazine Oxidation Assists Energy‐Efficient Hydrogen Evolution over a Bifunctional Cobalt Perselenide Nanosheet Electrode

Water electrolysis is a promising source of hydrogen; however, technological challenges remain. Intensive efforts have focused on developing highly efficient and earth-abundant electrocatalysts for water splitting. An effective strategy is proposed, using a bifunctional tubular cobalt perselenide nanosheet electrode, in which the sluggish oxygen evolution reaction is substituted with anodic hydrazine oxidation so as to assist energy-efficient hydrogen production. Specifically, this electrode produces a current density of 10 mA cm-2 at -84 mV for hydrogen evolution and -17 mV for hydrazine oxidation in 1.0 m KOH and 0.5 m hydrazine electrolyte. An ultralow cell voltage of only 164 mV is required to generate a current density of 10 mA cm-2 for 14 hours of stable water electrolysis.

Multivariate MOF-Templated Pomegranate-Like Ni/C as Efficient Bifunctional Electrocatalyst for Hydrogen Evolution and Urea Oxidation.

The production of hydrogen through electrolysis is considered as a feasible strategy to quench the world's clean-energy thirst. Compared with water electrolysis, urea electrolysis presents a more promising prospect in the way that it could carry out sewage treatment as well as energy-efficient hydrogen production at the same time. Herein, highly porous pomegranate-like Ni/C was synthesized from multivariate metal-organic frameworks and exhibits excellent hydrogen evolution activity with an unprecedented low overpotential of 40 mV at the current density of 10 mA cm-2 in 1 M KOH, ranking among the best earth-abundant electrocatalysts deposited on glassy carbon electrodes reported to date. In addition, it also displays superb anodic urea oxidation activity with an onset potential of 1.33 V vs RHE. Furthermore, a two-electrode urea electrolyzer with Ni/C as both the cathode and anode electrocatalyst was fabricated and generates 52 times more hydrogen than the water electrolyzer under the same conditions.