Hydrogen Adsorption Free Energy Research Articles

Coupling ceria with dual-phased molybdenum carbides for efficient and stable hydrogen evolution electrocatalysis at large-current-density in freshwater and seawater

In this study, we report a novel self-supported electrode consisting of ceria/molybdenum carbides composite microrods with adjustable crystalline phases and abundant heterostructures on carbon cloth (CeO2/MoxC/CC). The optimized CeO2/α-MoC/β-Mo2C MRs/CC electrode exhibits very low overpotentials of 22 and 29 mV at 10 mA cm−2 for hydrogen evolution reaction (HER) in alkaline freshwater and seawater, outperforming most of the reported molybdenum carbide-based electrocatalysts. Meanwhile, it could maintain long-term stability for over 100 h at a large current density of 1000 mA·cm−2. Theoretical study and experimental results reveal that the synergistic effects of α-MoC, β-Mo2C, and oxygen vacancy-rich CeO2 can effectively promote the dissociation of water molecules, tailor the d‐band electronic structure of MoxC with a thermoneutral hydrogen adsorption free energy, increase the numbers of active sites, and facilitate the vectorial electron transfer, thus achieving an enhanced HER performance. The CeO2/α-MoC/β-Mo2C MRs/CC electrode displays a potential large-scale application in hydrogen generation.

Interfacial engineering of Co-doped 1T-MoS2 coupled with V2C MXene for efficient electrocatalytic hydrogen evolution

Earth-abundant MoS2 has attracted great attentions as a promising hydrogen evolution reaction (HER) electrocatalyst, but it is limited by sluggish water dissociation and strong adsorption of the oxygen-containing intermediates in alkaline media. Herein, an interfacial engineering strategy to fabricate Co-doped 1T-MoS2 coupling with V2C MXene was reported to improve the HER kinetics of MoS2. DFT calculations predict that the construction of heterogeneous interfaces between V2C MXene and Co-doped 1T-MoS2 can effectively reduce the energy barrier of water dissociation and optimize the free energy of hydrogen adsorption. As a result, the synthesized Co-MoS2/V2C@CC nanohybrid exhibits excellent HER performance with small overpotentials of 70.1, 263.2 and 296 mV to achieve current densities of 10, 500 and 1000 mA cm−2, respectively, and outstanding stability for 50 h HER test without degradation. Additionally, the overall hydrazine-assisted water splitting (OHzS) system catalyzed by Co-MoS2/V2C@CC in both anode and cathode requires only 0.33 V to achieve a current density of 10 mA cm−2 with significant long-term durability.

Bixbyite-type Ln2O3 as promoters of metallic Ni for alkaline electrocatalytic hydrogen evolution

The active-site density, intrinsic activity, and durability of Ni-based catalysts are critical to their application in industrial alkaline water electrolysis. This work develops a kind of promoters, the bixbyite-type lanthanide metal sesquioxides (Ln2O3), which can be implanted into metallic Ni by selective high-temperature reduction to achieve highly efficient Ni/Ln2O3 hybrid electrocatalysts toward hydrogen evolution reaction. The screened Ni/Yb2O3 catalyst shows the low overpotential (20.0 mV at 10 mA cm−2), low Tafel slope (44.6 mV dec−1), and excellent long-term durability (360 h at 500 mA cm−2), significantly outperforming the metallic Ni and benchmark Pt/C catalysts. The remarkable hydrogen evolution activity and stability of Ni/Yb2O3 are attributed to that the Yb2O3 promoter with high oxophilicity and thermodynamic stability can greatly enlarge the active-site density, reduce the energy barrier of water dissociation, optimize the free energy of hydrogen adsorption, and avoid the oxidation corrosion of Ni.

Laser Shock Fabrication of Nitrogen Doped Inverse Spinel Fe3O4/Carbon Nanosheet Film Electrodes towards Hydrogen Evolution Reactions in Alkaline Media

The reliable and cost-effective production of high-performance film electrodes for hydrogen evolution reactions remains a challenge for the laser surface modification community. In this study, prior to a thermal imidization reaction, a small number of Fe3O4 nanoparticles were vortexed into a poly(amic acid) (PAA) prepolymer, and the achieved flat composite film was then ablated by a 1064 nm fiber laser. After laser irradiation, the hierarchical architectures of carbon nanosheets decorated with Fe3O4 nanoparticles were generated. Although pure polyimide (PI) film and laser carbonized PI film, as well as bare Fe3O4, showcase poor intrinsic catalytic activity toward alkaline hydrogen evolution reactions, our laser-derived Fe3O4/carbon nanosheet hybrid film demonstrated enhanced electrocatalytic activity and stability in 1 M KOH electrolyte; the overpotential(η10) reached 247 mV when the current density was 10 mA cm−2 with a slight current decay in the chronoamperometric examination of 12 h. Finally, we proposed that the substitution of N to O in Fe−O sites of trans spinel structured magnetite would be able to modulate the free energy of hydrogen adsorption (ΔGH*) and accelerate water dissociation.

BiO 2-x Nanosheets with Surface Electron Localizations for Efficient Electrocatalytic CO 2 Reduction to Formate

BiO _2-x Nanosheets with Surface Electron Localizations for Efficient Electrocatalytic CO ₂ Reduction to Formate

Enhanced visible light response of Ag/SnO2 nanostructure enables high-efficiency photocatalytic hydrogen evolution

Construction of synergistic photocatalysis system is regarded as an important concept for effectively utilizing solar energy. Herein, Ag nanoparticles decorated SnO2 flower-like structure is designed and fabricated to synergistically realize efficient hydrogen production from water splitting. According to the results of density functional theory simulations and corresponding experimental analyses, it is identified that interfacial charge coupling of composite system intrinsically facilitate the efficient interfacial charge migration and separation. Moreover, introducing Ag nanoparticles not only expands response range of incident light for SnO2 through LSPR effect but also reduces the hydrogen adsorption free energy in the catalytic process. Eventually, contributed by the enhanced interaction between reactants and catalysts and optimized carrier behavior, Ag/SnO2 exhibits a faster hydrogen production rate than SnO2. The research method designed in this paper may provide a new idea for research of photocatalyst for photocatalytic hydrogen evolution.

Highly Active Si Sites Enabled by Negative Valent Ru for Electrocatalytic Hydrogen Evolution in LaRuSi.

The discovery and identification of novel active sites are paramount for deepening the understanding of the catalytic mechanism and driving the development of remarkable electrocatalysts. Here, we reveal that the genuine active sites for the hydrogen evolution reaction (HER) in LaRuSi are Si sites, not the usually assumed Ru sites. Ru in LaRuSi has a peculiar negative valence state, which leads to strong hydrogen binding to Ru sites. Surprisingly, the Si sites have a Gibbs free energy of hydrogen adsorption that is near zero (0.063 eV). The moderate adsorption of hydrogen on Si sites during the HER process is also validated by in situ Raman analysis. Based on it, LaRuSi exhibits an overpotential of 72 mV at 10 mA cm-2 in alkaline media, which is close to the benchmark of Pt/C. This work sheds light on the recognition of real active sites and the exploration of innovative silicide HER electrocatalysts.

Highly Active Si Sites Enabled by Negative Valent Ru for Electrocatalytic Hydrogen Evolution in LaRuSi

AbstractThe discovery and identification of novel active sites are paramount for deepening the understanding of the catalytic mechanism and driving the development of remarkable electrocatalysts. Here, we reveal that the genuine active sites for the hydrogen evolution reaction (HER) in LaRuSi are Si sites, not the usually assumed Ru sites. Ru in LaRuSi has a peculiar negative valence state, which leads to strong hydrogen binding to Ru sites. Surprisingly, the Si sites have a Gibbs free energy of hydrogen adsorption that is near zero (0.063 eV). The moderate adsorption of hydrogen on Si sites during the HER process is also validated by in situ Raman analysis. Based on it, LaRuSi exhibits an overpotential of 72 mV at 10 mA cm−2 in alkaline media, which is close to the benchmark of Pt/C. This work sheds light on the recognition of real active sites and the exploration of innovative silicide HER electrocatalysts.

Controlling Reaction Routes in Noble‐Metal‐Catalyzed Conversion of Aryl Ethers

AbstractHydrogenolysis and hydrolysis of aryl ethers in the liquid phase are important reactions for accessing functionalized cyclic compounds from renewable feedstocks. On supported noble metals, hydrogenolysis is initiated by a hydrogen addition to the aromatic ring followed by C−O bond cleavage. In water, hydrolysis and hydrogenolysis proceed by partial hydrogenation of the aromatic ring prior to water or hydrogen insertion. The mechanisms are common for the studied metals, but the selectivity to hydrogenolysis increases in the order Pd<Rh<Ir<Ru≈Pt in decalin and water; the inverse was observed for the selectivity to hydrolysis in water. Hydrogenolysis selectivity correlates with the Gibbs free energy of hydrogen adsorption. Hydrogenolysis has the highest standard free energy of activation and a weak dependence on H2 pressure, thus, the selectivity to hydrogenolysis is maximized by increasing temperature and decreasing H2 pressure. Selectivity to C−O bond cleavage reaches >95 % in water and alkaline conditions.

Controlling Reaction Routes in Noble-Metal-Catalyzed Conversion of Aryl Ethers.

Hydrogenolysis and hydrolysis of aryl ethers in the liquid phase are important reactions for accessing functionalized cyclic compounds from renewable feedstocks. On supported noble metals, hydrogenolysis is initiated by a hydrogen addition to the aromatic ring followed by C−O bond cleavage. In water, hydrolysis and hydrogenolysis proceed by partial hydrogenation of the aromatic ring prior to water or hydrogen insertion. The mechanisms are common for the studied metals, but the selectivity to hydrogenolysis increases in the order Pd<Rh<Ir<Ru≈Pt in decalin and water; the inverse was observed for the selectivity to hydrolysis in water. Hydrogenolysis selectivity correlates with the Gibbs free energy of hydrogen adsorption. Hydrogenolysis has the highest standard free energy of activation and a weak dependence on H2 pressure, thus, the selectivity to hydrogenolysis is maximized by increasing temperature and decreasing H2 pressure. Selectivity to C−O bond cleavage reaches >95 % in water and alkaline conditions.

Ultrafast self-heating synthesis of robust heterogeneous nanocarbides for high current density hydrogen evolution reaction

Designing cost-effective and high-efficiency catalysts to electrolyze water is an effective way of producing hydrogen. Practical applications require highly active and stable hydrogen evolution reaction catalysts working at high current densities (≥1000 mA cm−2). However, it is challenging to simultaneously enhance the catalytic activity and interface stability of these catalysts. Herein, we report a rapid, energy-saving, and self-heating method to synthesize high-efficiency Mo2C/MoC/carbon nanotube hydrogen evolution reaction catalysts by ultrafast heating and cooling. The experiments and density functional theory calculations reveal that numerous Mo2C/MoC hetero-interfaces offer abundant active sites with a moderate hydrogen adsorption free energy ΔGH* (0.02 eV), and strong chemical bonding between the Mo2C/MoC catalysts and carbon nanotube heater/electrode significantly enhances the mechanical stability owing to instantaneous high temperature. As a result, the Mo2C/MoC/carbon nanotube catalyst achieves low overpotentials of 233 and 255 mV at 1000 and 1500 mA cm−2 in 1 M KOH, respectively, and the overpotential shows only a slight change after working at 1000 mA cm−2 for 14 days, suggesting the excellent activity and stability of the high-current-density hydrogen evolution reaction catalyst. The promising activity, excellent stability, and high productivity of our catalyst can fulfil the demands of hydrogen production in various applications.

Review on 2D Molybdenum Diselenide (MoSe2) and Its Hybrids for Green Hydrogen (H2) Generation Applications.

Hydrogen (H2) is a green and economical substitute to traditional fossil fuels due to zero carbon emissions. Water splitting technology is developing at a rapid speed to sustainably generate H2 through electro- and photolysis of water without the harmful emissions associated with steam methane reforming. Development of efficient catalysts for the hydrogen evolution reaction (HER) is pertinent for economical green H2 generation. In this regard, 2D transition metal dichalcogenides (TMDCs) are considered to be excellent alternatives to noble metal catalysts. Among other TMDCs, 2D MoSe2 is preferred due to the low Gibbs free energy for hydrogen adsorption, good electrical conductivity, and more metallic nature. Moreover, the physicochemical and electronic properties of MoSe2 can be easily tailored to suit HER application by simple synthetic strategies. Herein, we comprehensively review the application of 2D MoSe2 in the electrocatalytic HER, focusing on recent advancements in the modulation of the MoSe2 properties through nanostructure design, phase transformation, defect engineering, doping, and formation of heterostructures. We also discuss the role of 2D MoSe2 as a cocatalyst in the photocatalytic HER. The article concludes with a synopsis of current progress and prospective future trends.

Atomic‐Level Platinum Filling into Ni‐Vacancies of Dual‐Deficient NiO for Boosting Electrocatalytic Hydrogen Evolution

AbstractDeveloping low‐cost and high‐efficiency catalysts for sustainable hydrogen production through electrocatalytic hydrogen evolution reaction (HER) is crucial yet remains challenging. Here, a strategy is proposed to fill Ni‐vacancy (Niv) sites of dual‐deficient NiO (D‐NiO‐Pt) deliberately created by Ar plasma with homogeneously distributed Pt atoms driven by oxygen vacancies (Ov). The incorporated Pt atoms filling the Niv reduce the formation energy to increase crystal stability, and subsequently combine with additional Ov to tune the electronic structure of the surrounding Ni sites. Thus, a more ideal hydrogen adsorption free energy (ΔGH*) closer to 0 of Ni sites and Pt sites can be achieved. As a result, the D‐NiO‐Pt electrode achieves superior mass activity of ≈1600 mA mg−1 (normalized by platinum) and nearly negligible loss of activity during long‐term operation, which is much better than as‐prepared Pt‐containing NiO catalysts without plasma treatment. A low overpotential of 20 mV is required for the D‐NiO‐Pt at 10 mA cm−2 in alkaline HER, outperforming that of the commercial Pt/C. In addition, the universal access to the other Ni‐based compounds including nickel phosphide (Ni2P), nickel sulfide (Ni0.96S), and nickel selenide (NiSe2) is also demonstrated by employing a vacancy‐driven Pt filling mechanism.

Phase-Selective Synthesis of Ruthenium Phosphide in Hybrid Structure Enables Efficient Hybrid Water Electrolysis Under pH-Universal Conditions.

Hydrazine-assisted hybrid water electrolysis is an energy-saving approach to produce high-purity hydrogen, whereas the development of pH-universal bifunctional catalysts encounters a grand challenge. Herein, a phase-selective synthesis of ruthenium phosphide compounds hybrid with carbon forming pancake-like particles (denoted as Rux P/C-PAN, x= 1 or 2) is presented. The obtained RuP/C-PAN exhibits the highest catalytic activity among the control samples, delivering ultralow cell voltages of 0.03, 0.27, and 0.65V to drive 10mAcm-2 using hybrid water electrolysis corresponding to pH values of 14, 7, and 0, respectively. Theoretical calculation deciphers that the RuP phase displays optimized free energy for hydrogen adsorption and reduced energy barrier for hydrazine dehydrogenation. This work may not only open up a new avenue in exploring universally compatible catalyst to transcend the limitation on the pH value of electrolytes, but also push forward the development of an energy-saving hydrogen generation technique based on emerging hybrid water electrolysis.

Boron-doped CoSe2 nanowires as high-efficient electrocatalyst for hydrogen evolution reaction

High activity and stable hydrogen evolution reaction (HER) catalysts have an indispensable influence on hydrogen production. Pyrite cobalt selenide (CoSe2) is considered an excellent non-noble metal compound HER catalyst due to its low price and excellent electrical conductivity. However, the HER catalytic activity of CoSe2 is still not ideal because of the weak adsorption of hydrogen on its active Co site. The anion introduction can improve the electronic structure of the catalyst and thereby enhance the performance of HER. Here, we report that B-doped CoSe2 nanomaterials on carbon cloth (B-CoSe2/CC) were successfully synthesized. Compared with CoSe2, B-CoSe2 exhibits better HER performance in 1 M KOH. The overpotential of B-CoSe2 catalyst is only 153 mV at 10 mA cm−2. Tafel slope of B-CoSe2/CC sample is only 85 mV dec−1. In addition, B-CoSe2/CC exhibits perfect long-term durability and cycle stability. Density functional theory (DFT) calculations illustrate that the doping of B improves the intrinsic conductivity of CoSe2 and optimizes the hydrogen adsorption free energy (ΔGH*) of Se and Co sites. This work not only proposes a new anion doping strategy to improve the electronic structure of cobalt-based selenides for improved HER performance, but also provides a reference for the screening and design of other transition metal compound HER electrocatalysts.

Reduction of Transition-Metal Columbite-Tantalite as a Highly Efficient Electrocatalyst for Water Splitting

We successfully report a liquid-liquid chemical reduction and hydrothermal synthesis of a highly stable columbite-tantalite electrocatalyst with remarkable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance in acidic media. The reduced Fe0.79Mn0.21Nb0.16Ta0.84O6 (CTr) electrocatalyst shows a low overpotential of 84.23 mV at 10 mA cm-2 and 103.7 achieved at 20 mA cm-2 current density in situ for the HER and OER, respectively. The electrocatalyst also exhibited low Tafel slopes of 104.97 mV/dec for the HER and 57.67 mV/dec for the OER, verifying their rapid catalytic kinetics. The electrolyzer maintained a cell voltage of 1.5 V and potential-time stability close to that of Pt/C and RuO2. Complementary first-principles density functional theory calculations identify the Mn sites as most active sites on the Fe0.75Mn0.25Ta1.875Nb0.125O6 (100) surface, predicting a moderate Gibbs free energy of hydrogen adsorption (ΔGH* ≈ 0.08 eV) and a low overpotential of η = 0.47 V. The |ΔGMnH*| = 0.08 eV on the Fe0.75Mn0.25Ta1.875Nb0.125O6 (100) surface is similar to that of the well-known and highly efficient Pt catalyst (|ΔGPtH*| ≈ 0.09 eV).

Tailoring photoactivity of polymeric carbon nitride via donor-π-acceptor network

Molecular doping approach can effectively modulate the charge transfer kinetics of polymeric carbon nitride (PCN) photocatalyst. Herein, we show that doping of PCN with a strong electron-withdrawing 2,3-diaminopyridine (DAP) induces the formation of donor-π-acceptor (D-π-A) network. As formed D-π-A type network demonstrated a photocatalytic hydrogen production activity of 6.56 mmolg−1 h−1, which is 4.5-times greater than the pure PCN. The optoelectronic features characterized by spectroscopic techniques indicate rapid separation of photoexcited charge carriers and extended light-harvesting ability of DAP-doped PCN. Further, the theoretical analysis revealed that DAP-doped PCN has near-ideal hydrogen adsorption free energy of − 0.11 eV, which supports the excellent hydrogen production performance. Importantly, the hydrogen production activity demonstrated here outperforms several state-of-art molecular-doped PCN-based catalysts. This study sheds light on the effective production of PCN-based D-π-A networks using conjugated heterocyclic compounds.

Single-atom Ir and Ru anchored on graphitic carbon nitride for efficient and stable electrocatalytic/photocatalytic hydrogen evolution

Renewable energy-powered water electrolysis and photocatalytic water splitting are two promising approaches to green hydrogen production. Electrocatalysts and photocatalysts are essential components determining the performance of water electrolyzers and photocatalytic reactors, respectively. Currently, there is a pressing need to develop efficient and stable electrocatalysts and photocatalysts for large-scale deployment of these devices to reach carbon neutrality. Herein, we report the synthesis of single-atom Ir and Ru anchored on mesoporous graphitic carbon nitride (Ir-g-CN and Ru-g-CN), which can be used as electrocatalysts and photocatalysts for the hydrogen evolution reaction (HER). Remarkably, Ru-g-CN shows a high turnover frequency (TOF) of 12.9 and 5.1 s−1 at an overpotential (η) of 100 mV in 0.5 M H2SO4 and 1.0 M KOH, respectively, outperforming Ir-g-CN, commercial Pt/C benchmark and many other advanced HER catalysts reported recently. Moreover, Ru-g-CN can deliver an exceptionally high mass activity of 24.55 and 8.78 A mg−1 at η = 100 mV in acidic and alkaline solutions, meanwhile exhibiting a high apparent current density, which is favorable for practical applications. Additionally, both Ru-g-CN and Ir-g-CN show outstanding catalytic stability, continuously catalyzing the HER in acidic and alkaline conditions for 120 h with minimal degradation. Besides, when used for photocatalytic water splitting, Ru-g-CN can achieve a high hydrogen production rate of 489.7 mmol H2 gRu−1 h−1, and shows good photocatalytic stability. Our density functional theory (DFT) calculations demonstrate that loading Ir and Ru single-atoms on g-CN alters the electronic structure, resulting in a reduced bandgap and improved electrical conductivity, facilitating electron transfer during the catalysis. Moreover, the Gibbs free energy of hydrogen adsorption on Ru-g-CN and Ir-g-CN is also substantially lowered, enhancing HER performance.

Asymmetric surfaces endow Janus bismuth oxyhalides with enhanced electronic and catalytic properties for the hydrogen evolution reaction

The electronic and catalytic properties of Janus bismuth oxyhalide (Bi2O2XY, where X/Y = Cl, Br, or I, and X ≠ Y) for the hydrogen evolution reaction (HER) are evaluated through first-principles calculations. Janus Bi2O2XY shows an enhanced separation efficiency of electron−hole pairs and an augmented utilization of solar energy due to Janus asymmetry. The asymmetric halogen surfaces on both sides of Janus Bi2O2XY induce an electrostatic potential difference, which leads to a staggered band alignment. The solar-to-hydrogen (STH) efficiencies of Janus Bi2O2BrI and Bi2O2ClI have greatly improved compared to those of pristine BiOBr and BiOCl. Additionally, Janus Bi2O2XY achieves stronger internal electric fields (IEFs) and a more suitable Gibbs free energy of hydrogen adsorption (ΔGH) than pristine BiOX. Moreover, the halogen layer with a smaller electronegativity in Janus Bi2O2XY forms a stronger IEF with the oxygen layer; consequently, the ΔGH of terminations value is closer to the ideal value for the HER. The localized edge states in the p-orbital density of states (DOS) projected onto O atoms are responsible for the HER activity of terminations. This work provides a comprehensive understanding of Janus Bi2O2XY for the HER and provides a strategy for improving photocatalysis.

Enhanced effect of H2O monolayer on metal doped nitrogen-containing graphene for hydrogen evolution reactions

H 2 O-covered effect strongly enhanced ΔG(H*) Gibbs free energy of hydrogen adsorption, and two different types of H 2 formation and desorption are observed. • H 2 O-covered effect strongly enhanced ΔG(H*) Gibbs free energy. • Two different types of H 2 formation and desorption are observed. • A careful comparison between the explicit and implicit solvent models is made. The widely-held MN 4 @GR (metal doped nitrogen-contained graphene) model with low ΔG(H*) Gibbs free energy of hydrogen adsorption has attracted much attention because of excellent performance in hydrogen evolution reaction (HER). Besides of the common descriptor of ΔG(H*), we present another additional descriptor of H 2 formation and desorption energy barriers on eight MN x @GR (M = Fe, Co, Rh, Ir, Ni, Pd, Pt, and Cu; x = 0–4) catalysts with and without H 2 O-covered effect. Using density functional theory calculations, ΔG(H*) is strongly enhanced with almost one order of magnitude in the presence of the H 2 O-covered effect. Two different types of H 2 formation and desorption are observed on these eight MN x @GRs with labelling as the one-step and two-step desorption mechanisms. The H 2 O-covered FeN 4 @GR and H 2 O-covered CuN 4 @GR represent two different desorption types with the lowest diffusion and desorption barriers, which indicates the best HER performance.