Improved Hydrogen Evolution Reaction Research Articles

Understanding Performance Limitation of Liquid Alkaline Water Electrolyzers

Liquid alkaline water electrolyzers (LAWEs), being the most commercially mature electrolysis technology, play a pivotal role in large-scale hydrogen production. However, LAWEs suffer from low operational efficiency, primarily due to un-optimized electrode structure and chemical compositions. Thus, we investigated how various electrode configurations could impact LAWE performance. Our results show that Ni felt electrodes outperform the conventional Ni foam thanks to improved electrochemical active surface area (ECSA) and preferred electrode surface structure that minimizes the micro-gaps in between the electrode and separator. By comparing the stainless steel (SS) felt electrodes with Ni felt electrodes, SS not only shows better oxygen evolution reaction activity but also improved hydrogen evolution reaction activity, which is less studied in the literature. We also show that a bilayer structure with small pore radius facing the separator could further improve LAWE performance by further optimizing interfacial contact between electrode and separator. These findings enable LAWEs to sustain 2 A cm−2 at 2.2 V and operate steadily at 1 A cm−2 for nearly 600 h with negligible performance decay. Our studies establish criteria for selecting electrodes to achieve high-performance LAWE and, in turn, expedite the adoption of LAWEs in hydrogen production and the transition towards low-carbon economies.

MoS2 supported Ruthenium nanoparticles with abundant sulfur vacancies significantly improved hydrogen evolution reaction

The electrochemical hydrogen evolution reaction (HER) has become one of effective ways to produce hydrogen. MoS2 is a promising electrocatalyst for the HER, and loading noble metal atoms on MoS2 support can further enhance its HER activity. In present work, the CO was employed as a structure-directing agent to in situ synthesize MoS2-n (n = 0, 0.5, 1.0, 1.4 and 2.0 MPa, representing the CO pressure). Among them, the MoS2-1.4 with highest amounts of sulfur vacancies and superior alkaline HER performance was selected as the support for Ru loadings. Sulfur vacancies can stabilize Ru nanoparticles, prevent nanoparticles from aggregating, and facilitate the formation of small-sized nanoparticles. By optimizing the loading amounts of Ru, the 5Ru@MoS2-1.4 with the Ru loading of 5 wt.% and nanoparticle size of 2 nm exhibits the best alkaline HER activity by displaying a low overpotential of 55 mV and Tafel slope of 68.6 mV dec−1 at a current density of 10 mA cm−2 in 1.0 M KOH medium. This can be majorly related to the synergistic effect of MoS2-1.4 support and small-sized Ru nanoparticles, wherein the CO plays a significant role in regulating the structure of MoS2-1.4 support that favors dispersion of Ru nanoparticles. Generally, present work provides a strategy to enhance the HER catalytic performance of MoS2, which is favorable for other highly-efficient catalyst design.

Improving hydrogen evolution reaction efficiency through lattice tuning

Improving hydrogen evolution reaction efficiency through lattice tuning

Atomically Precise Mo2Cu17 Bimetallic Nanocluster: Synergistic Mo2O4-Coupled Copper Alkynyl Cluster for the Improved Hydrogen Evolution Reaction Performance.

Electrolytic hydrogen production via water splitting holds significant promise for the future of the energy revolution. The design of efficient and abundant catalysts, coupled with a comprehensive understanding of the hydrogen evolution reaction (HER) mechanism, is of paramount importance. In this study, we propose a strategy to craft an atomically precise cluster catalyst with superior HER performance by cocoupling a Mo2O4 structural unit and a Cu(I) alkynyl cluster into a structured framework. The resulting bimetallic cluster, Mo2Cu17, encapsulates a distinctive structure [Mo2O4Cu17(TC4A)4(PhC≡C)6], comprising a binuclear Mo2O4 subunit and a {Cu17(TC4A)2(PhC≡C)6} cluster, both shielded by thiacalix[4]arene (TC4A) and phenylacetylene (PhC≡CH). Expanding our exploration, we synthesized two homoleptic CuI alkynyl clusters coprotected by the TC4A and PhC≡C- ligands: Cu13 and Cu22. Remarkably, Mo2Cu17 demonstrates superior HER efficiency compared to its counterparts, achieving a current density of 10 mA cm-2 in alkaline solution with an overpotential as low as 120 mV, significantly outperforming Cu13 (178 mV) and Cu22 (214 mV) nanoclusters. DFT calculations illuminate the catalytic mechanism and indicate that the intrinsically higher activity of Mo2Cu17 may be attributed to the synergistic Mo2O4-Cu(I) coupling.

Insights of the efficient hydrogen evolution reaction performance in bimetallic Au4Cu2 nanoclusters.

The design of efficient electrocatalysts for improving hydrogen evolution reaction (HER) performance using atomically precise metal nanoclusters (NCs) is an emerging area of research. Here, we have studied the HER electrocatalytic performance of monometallic Cu6 and Au6 nanoclusters and bimetallic Au4Cu2 nanoclusters. A bimetallic Au4Cu2/MoS2 composite exhibits excellent HER catalytic activity with an overpotential (η10) of 155 mV vs. reversible hydrogen electrode observed at 10 mA cm-2 current density. The improved HER performance in Au4Cu2 is due to the increased electrochemically active surface area (ECSA), and Au4Cu2 NCs exhibits better stability than Cu6 and Au6 systems and bare MoS2. This augmentation offers a greater number of active sites for the favorable adsorption of reaction intermediates. Furthermore, by employing X-ray photoelectron spectroscopy (XPS) and Raman analysis, the kinetics of HER in the Au4Cu2/MoS2 composite were elucidated, attributing the favorable performance to better electronic interactions occurring at the interface between Au4Cu2 NCs and the MoS2 substrate. Theoretical analysis reveals that the inherent catalytic enhancement in Au4Cu2/MoS2 is due to favorable H atom adsorption over it and the smallest ΔGH* value. The downshift in the d-band of the Au4Cu2/MoS2 composite influences the binding energy of intermediate catalytic species. This new catalyst sheds light on the structure-property relationship for improving electrocatalytic performance at the atomic level.

First synthesis of RuSn solid-solution alloy nanoparticles and their enhanced hydrogen evolution reaction activity.

Solid-solution alloys based on platinum group metals and p-block metals have attracted much attention due to their promising potential as materials with a continuously fine-tunable electronic structure. Here, we report on the first synthesis of novel solid-solution RuSn alloy nanoparticles (NPs) by electrochemical cyclic voltammetry sweeping of RuSn@SnOx NPs. High-angle annular dark-field scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy maps confirmed the random and homogeneous distribution of Ru and Sn elements in the alloy NPs. Compared with monometallic Ru NPs, the RuSn alloy NPs showed improved hydrogen evolution reaction (HER) performance. The overpotentials of Ru0.94Sn0.06 NPs/C and Ru0.87Sn0.13 NPs/C to achieve a current density of 10 mA cm-2 were 43.41 and 33.19 mV, respectively, which are lower than those of monometallic Ru NPs/C (53.53 mV) and commercial Pt NPs/C (55.77 mV). The valence-band structures of the NPs investigated by hard X-ray photoelectron spectroscopy demonstrated that the d-band centre of RuSn NPs shifted downward compared with that of Ru NPs. X-ray photoelectron spectroscopy and X-ray absorption near-edge structure analyses indicated that in the RuSn alloy NPs, charge transfer occurs from Sn to Ru, which was considered to result in a downward shift of the d-band centre in RuSn NPs and to regulate the adsorption energy of intermediate Hads effectively, and thus enable the RuSn solid-solution alloy NPs to exhibit excellent HER catalytic properties.

Modulating the electronic structure of MoS2 nanosheets by Mn doping for improving hydrogen evolution reaction: an experimental and theoretical DFT-QTAIM study

This study provides experimental and theoretical analyses of the effects of Mn doping on the electronic structure of MoS2 nanosheets and its impact on the performance of the hydrogen evolution reaction (HER). Experiments show that Mn doping alters the electronic structure of MoS2. This leads to an enhanced HER activity. The Mn-MoS2 nanosheets with a Mn/Mo molar ratio of 1:15 exhibit an overpotential of approximately 238 mV at a current density of 10 mA/cm2 and a low Tafel slope of 68 mV/decade in 0.5 M H2SO4. Density Functional Theory calculations and Bader analysis indicate that the incorporation of Mn atoms into the basal plane of MoS2 nanosheets activates all in-plane S atom sites and three Mo atoms neighboring the Mn dopant, thereby reducing the adsorption free energy of H atoms. Further, the Mn dopant enhances the intrinsic electronic conductivity of MoS2 by reducing its bandgap, which leads to a rapid charge transfer across the basal plane during H2 evolution.

Effect of electron transfer of 2D Ti3C2Tx@MOF heterostructure on hydrogen evolution reaction activity

Metal-organic framework (MOF) layers were grown in situ from 2D transition metal carbides (MXenes, Ti3C2Tx) at room temperature to obtain the two-dimensional (2D) Ti3C2Tx@MOF heterostructures with a tightly connected interface. This interface provided more titanium atoms in the low-valence state in comparison to the original Ti3C2Tx, thus facilitating more electron transfer from Ti3C2Tx to MOF-(Fe/Co) nanosheets. The charge density difference and density functional theory results disclosed that Ti3C2Tx could modulate the electronic density around the active sites and lower ΔGH* energy barrier of 2D MOF-(Fe/Co) nanosheets towards the improved hydrogen evolution reaction (HER) activity. The obtained 2D Ti3C2Tx@MOF heterostructures exhibited a much higher HER activity in 1 M KOH electrolyte (with the overpotential of 104 mV at 10 mA/cm2 and Tafel slope of 79 mV/dec) than those of 2D Ti3C2Tx@MOF-TH, 2D MOF nanosheets, and Ti3C2Tx nanosheets. This research provides a basis for developing superior 2D MOFs, which can enhance HER properties through efficient electronic transport at the heterojunction interface.

Influence of antisite defects on two-dimensional polymeric material for improved hydrogen evolution reaction

Two-dimensional materials (2D) supported by single atom catalysis have emerged as effective catalysts for H2 production at large scale by Hydrogen Evolution Reaction (HER). While there is a research surge on utilizing inexpensive metals as catalysts to replace Platinum (Pt) and other related noble metals, their practical limitations such as oxidation issues remain a concern. In this work, we report electrochemical HER activity of a recently synthesized metal-free 2D Polyaramid (2DPA) using Density Functional Theory (DFT) calculations. Pristine 2DPA exhibits remarkable HER performance in terms of active sites availability for hydrogen adsorption and the lowest Gibb's free energy change (−0.06 eV) close to that of benchmark Pt/C catalyst (−0.09 eV). Furthermore, introduction of antisite defects by substituting carbon for nitrogen (CN) and nitrogen for carbon (NC) in pristine 2DPA depicts enhanced HER activity. CN and NC defects tune the electronic properties by reducing the band gap resulting improved conductivity. Low formation energies calculated for obtaining antisite defects confirm their feasibility of synthesis while ab initio molecular dynamics (AIMD) simulations ensure their thermal stability at room temperature. The change in Gibb's free energy (ΔGH) values for CN-defective and NC-defective 2DPA are computed to be −0.13 eV and −0.11 eV, respectively. Both CN-defective and NC-defective 2DPA favor H2 evolution via Heyrovsky reaction pathways due to their relatively lower activation energy, 0.64 eV and 0.51 eV, respectively. Our findings encourage design and development of a novel 2D metal-free electrocatalyst for enhanced HER.

Ruthenium nanoparticles incorporated hollow carbon nanoshells for improved hydrogen evolution reaction

The development of efficient and stable catalyst is crucial for hydrogen evolution reaction (HER) in water electrolysis. The rational design of porous supports can effectively improve the exposure of active sites and increase the electrochemically active surface area of catalysts. In this study, a nanostructured carbon nanoshell (CS) is proposed for the synthesis of ruthenium and nitrogen incorporated carbon catalyst (CS@N-Ru) catalysts. Physicochemical characterization show that the prepared catalyst exhibits a hollow structure and abundant nitrogen/ruthenium related active sites, which enables the improvement of mass transfer and the catalytic activity. The electrochemical tests show that the prepared CS remarkably facilitates the performance of catalyst, the CS@N-Ru500 synthesized at 500 °C exhibits the best catalytic activity with a low overpotential of 35 mV at 10 mA/cm2 and Tafel slope of 38 mV/dec, attributing to the increased electrochemically active surface area, reduced electron/ion transfer resistance, and accelerated kinetics of HER. These findings suggest that the CS@N-Ru can be a promising alternative to Pt/C for HER in water electrolysis.

Non-covalent interaction of atomically dispersed dual-site catalysts featuring Co and Ni nascent pair sites for efficient electrocatalytic overall water splitting

The scarcity of highly effective and economical catalysts is a major impediment to the widespread adoption of electrochemical water splitting for the generation of hydrogen. MoS2, a low-cost candidate, suffers from inefficient catalytic activity. Nonetheless, a captivating strategy has emerged, which involves the engineering of heteroatom doping to enhance electrochemical proficiency. This investigation demonstrates a successful implementation of the strategy by combining ultrathin MoS2 nanosheets with Co and Ni dual single multi-atoms (DSMAs) grown directly on 2D N-doped carbon nanosheets (CoNi-MoS2/NCNs) for the purpose of improving hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). With the aid of a dual-atom doped bifunctional electrocatalyst, effective water splitting has been achieved across a broad pH range in electrolytes. The double doping of Co and Ni strengthens their interactions, thereby altering the electromagnetic composition of the host MoS2 and ultimately leading to improved electrocatalytic activity. Additionally, the synergistic effect between NCNs and MoS2 nanosheets provided efficient electron transport channels for ions and an ample surface area with open voids for ion diffusion. Consequently, the CoNi-MoS2/NCNs catalysts demonstrated exceptional stability and activity, producing low degree overpotentials of 180.5, 124.9, and 196.4 mV for HER and 200, 203, and 207 mV for OER in neutral, alkaline, and acidic mediums, respectively, while also exhibiting outstanding overall water-splitting performance, durability, and stability when used as an electrolyzer at universal pH.

Discrepancy of alkaline/neutral hydrogen evolution activity from NiCoSe2/NC and Co–NiSe/NC derived from in-situ thermal and solution processing selenizations of ZIF-67

Constructing cobalt-based selenide catalyst with accessible active site and superior charge transfer capability by simultaneous tailoring chemical component and structure through the feasible strategy is the key to display improved hydrogen evolution reaction (HER) activity. Herein, the bimetal NiCoSe2/nitrogen-doped carbon (NC) with novel flake structure (NiCoSe2/NC/NF) and particle-like cobalt-doped NiSe/NC (Co–NiSe/NC/NF) were synthesized by the in-situ thermal and solution processing selenizations of ZIF-67/NF, respectively. The intrinsic catalytic activity of NiCoSe2, the further accelerated charge-transfer capability originated from the fresh NC and two-dimensional layer structure, and mutually reinforcing kinetics from the closely integrated NiCoSe2 nanoparticles and NC plate endow NiCoSe2/NC/NF with 141 and 284 mV to reach 10 mA cm−2 under alkaline and neutral electrolytes, respectively, accompanying with Tafel slope of 109 and 206 mV dec−1, which were obviously higher than that of the HER properties of Co–NiSe/NC/NF (η10 = 179 mV and Tafel slope of 127 mV dec−1 at alkaline condition, η10 = 301 mV and Tafel slope of 235 mV dec−1 at neutral condition). Meanwhile, the NiCoSe2/NC/NF and Co–NiSe/NC/NF were exhibited well electrochemical stability under alkaline/neutral conditions. This study offers practicable strategy for intuitive comparing the influence of selenization procedures on the whole alkaline/neutral HER activity of cobalt-based catalysts.

Improving hydrogen evolution catalytic activity of 2D carbon allotrope biphenylene with B, N, P doping: Density functional theory investigations

Using a first principles approach, we studied the hydrogen evolution reaction activity of newly synthesized biphenylene and B, N, P decorated biphenylene sheet. Hydrogen evolution reaction activity of pristine biphenylene sheet is not encouraging, as it is similar to pristine graphene. The Gibbs free energy and overpotential of P(N) doped on biphenylene sheet are 0.022 (−0.092) eV and 22 (92) mV, respectively. The reported Gibbs free energy and overpotential of Pt are 0.9 eV and 90 mV. Hence doping of P(N) atom on top of biphenylene sheet improves hydrogen evolution reaction activity much better (near to) Pt metal. We analyzed the adsorption mechanism of dopants (B, N, P) and hydrogen with Bader charge analysis and density of states analysis. P and N-decoration on biphenylene sheet change its electronic structure so that one obtains improved hydrogen evolution reaction activity for P and N-doped biphenylene sheet. Furthermore, the stability of N, P decorated biphenylene at room temperature with ab-initio molecular dynamics and formation energy near that of biphenylene indicate experimental feasibility. We have compared all our best hydrogen evolution reaction activity results in the reaction coordinate and volcano plots of pristine, B, N, and P-doped BPh sheets. They indicate that P-doped biphenylene is a metal-free, powerful catalyst for hydrogen evolution reaction activities.

Construction of Ni4Mo/MoO2 heterostructure on oxygen vacancy enriched NiMoO4 nanorods as an efficient bifunctional electrocatalyst for overall water splitting

Despite great efforts over the past decade, rational design of bifunctional electrocatalysts with low cost and high efficiency still remains a challenge to achieve industrial water splitting. Herein, we synthesized the nickel-molybdenum nanorod array catalyst supported on NF (NMO@NM/MO) by a two-step process of hydrothermal and reductive annealing. Partial reduction of the NiMoO4 induces the structural reconstruction and formation of the Ni4Mo/MoO2 heterostructure on oxygen vacancy enriched nanorod, which bring out sufficient active sites, large specific surface area and favorable interfacial charge transfer. Thanks to the unique core–shell structure with the heterostructured Ni4Mo/MoO2 surface and defect-rich NiMoO4 core, the obtained electrocatalyst shows greatly improved hydrogen evolution reaction (HER) activity with an ultralow overpotential of 63 mV at 100 mA cm−2 (vs. 314 mV for the NiMoO4). Density function theory calculations reveal that the construction of the Ni4Mo/MoO2 heterostructure effectively accelerates H2O dissociation kinetics, while the defective NiMoO4 facilitates H* adsorption/desorption. Moreover, the heterostructure catalyst also displays excellent oxygen evolution reaction (OER) performance with the low overpotential of 274 mV at 100 mA cm−2. When coupling HER and OER by using NMO@NM/MO as both the cathode and anode, the alkaline electrolyzer delivers a current density of 10 mA cm−2 at only 1.50 V as well as good robustness. The synergistic effect of the hetero-interface and the defect engineering endows the electrocatalyst with excellent bifunctional catalytic activity for HER and OER. This work may provide a route for rational design of heterostructure electrocatalysts with multiple active components.

Doped MoS2 Polymorph for an Improved Hydrogen Evolution Reaction.

Green hydrogen produced from solar energy could be one of the solutions to the growing energy shortage as non-renewable energy sources are phased out. However, the current catalyst materials used for photocatalytic water splitting (PWS) cannot compete with other renewable technologies when it comes to efficiency and production cost. Transition-metal dichalcogenides, such as molybdenum disulfides (MoS2), have previously proven to have electronic and optical properties that could tackle these challenges. In this work, optical properties, the d-band center, and Gibbs free energy are calculated for seven MoS2 polymorphs using first-principles calculations and density functional theory (DFT) to show that they could be suitable as photocatalysts for PWS. Out of the seven, the two polymorphs 3Ha and 2R1 were shown to have d-band center values closest to the optimal value, while the Gibbs free energy for all seven polymorphs was within 5% of each other. In a previous study, we found that 3Hb had the highest electron mobility among all seven polymorphs and an optimal bandgap for photocatalytic reactions. The 3Hb polymorphs were therefore selected for further study. An in-depth analysis of the enhancement of the electronic properties and the Gibbs free energy through substitutional doping with Al, Co, N, and Ni was carried out. For the very first time, substitutional doping of MoS2 was attempted. We found that replacing one Mo atom with Al, Co, I, N, and Ni lowered the Gibbs free energy by a factor of 10, which would increase the hydrogen evolution reaction of the catalyst. Our study further shows that 3Hb with one S atom replaced with Al, Co, I, N, or Ni is dynamically and mechanically stable, while for 3Hb, replacing one Mo atom with Al and Ni makes the structure stable. Based on the low Gibbs free energy, stability, and electronic bandgap 3Hb, MoS2 doped with Al for one Mo atom emerges as a promising candidate for photocatalytic water splitting.

Amorphous nickel hydroxide shell tailors local chemical environment on platinum surface for alkaline hydrogen evolution reaction.

In analogy to natural enzymes, an elaborated design of catalytic systems with a specifically tailored local chemical environment could substantially improve reaction kinetics, effectively combat catalyst poisoning effect and boost catalyst lifetime under unfavourable reaction conditions. Here we report a unique design of 'Ni(OH)2-clothed Pt-tetrapods' with an amorphous Ni(OH)2 shell as a water dissociation catalyst and a proton conductive encapsulation layer to isolate the Pt core from bulk alkaline electrolyte while ensuring efficient proton supply to the active Pt sites. This design creates a favourable local chemical environment to result in acidic-like hydrogen evolution reaction kinetics with a lowest Tafel slope of 27 mV per decade and a record-high specific activity and mass activity in alkaline electrolyte. The proton conductive Ni(OH)2 shell can also effectively reject impurity ions and retard the Oswald ripening, endowing a high tolerance to solution impurities and exceptional long-term durability that is difficult to achieve in the naked Pt catalysts. The markedly improved hydrogen evolution reaction activity and durability in an alkaline medium promise an attractive catalyst material for alkaline water electrolysers and renewable chemical fuel generation.

Joule heating synthesis of well lattice-matched Co2Mo3O8/MoO2 heterointerfaces with greatly improved hydrogen evolution reaction in alkaline seawater electrolysis with 12.4 % STH efficiency

Herein, through a rapid Joule heating method, we have successfully prepared well lattice-matched Co2Mo3O8/MoO2 heterointerfaces on Ni foam (Co2Mo3O8/MoO2/NF) in only 130 s. Notably, the rapid Joule heating can effectively avoid oxidation of catalyst caused by prolonged heating and achieve rich uncoordinated Mo4+ sites, which contributed to the enhanced electrocatalytic performance in hydrogen evolution reaction (HER). As-prepared Co2Mo3O8/MoO2 delivered remarkable HER activity (23 mV at 10 mA cm−2), which was comparable to Pt-based electrocatalyst. As-prepared sample also revealed excellent stability at 200-h test in electrocatalytic splitting of alkaline seawater. Of particular note, the solar-driven H2O-H2 electrolyzer also showed a promising solar-to-hydrogen (STH) efficiency of 12.4 %. The cell voltage for the home-made anion exchange membrane (AEM) seawater electrolyzer was only 2.13 V at 200 mA·cm−2 at 50 °C, and only 4.7 kW-h required to produce 1 m3 of H2. DFT calculations revealed that the electron redistribution spontaneously takes place at Co–O–Mo bonds at Co2Mo3O8/MoO2 heterointerfaces, which could regulate the electronic structure and d-band center of Mo sites, and then achieve high-efficiency adsorption of H2O on Mo sites and near-zero hydrogen-adsorption free energy on O sites. This study provided a new strategy to regulate the chemical states via Joule heating for highly efficient seawater splitting to evolve H2.

Activating MoS2 by site-selective Ni incorporation for efficient and robust alkaline hydrogen evolution

In this work, a surface engineering strategy has been developed to implant atomic Ni mostly enriched in 1 nm thickness of MoS2 nanosheets, and suppresses the segregation of undesired NiSx. Notably, this structural regulation not only creates additional edges exposed at the inert basal plane of MoS2 nanosheets, but also increases the catalytic ability of edge sites by forming dominant NiMoS phase. As such, a low overpotential of 95 mV is achieved to deliver a current density of 10 mA cm−2, which is 242 mV decrease than unmodified MoS2, together with 86.5% preservation of initial capacity after 100 h test. Theoretical calculations further identify the activated catalytic sites both in Mo-edge and S-edge, and the specific atomic configurations enable the synergistic effect to optimize the adsorption-desorption of H∗, and is responsible for the remarkably improved hydrogen evolution reaction (HER) activity.

Ru-loaded pyrrolic-N-doped extensively graphitized porous carbon for high performance electrochemical hydrogen evolution

Herein, we report a novel methodology for preparation of new N-doped extensively graphitized porous carbon (N-GPC) as a new catalyst support for Ru nanoparticles (NPs) with dramatically improved hydrogen evolution reaction (HER) activity. Our method is remarkably simple: pyrolyzing g-C3N4 in the presence of Mg metal. Here, we show that Mg plays marvelous dual roles as a reducing agent to graphitize the g-C3N4 precursor at low temperature and as a precursor for Mg3N2, which generates network-structured porous carbon as a new porogen. This offers highly robust graphitized carbon with high electrical conductivity, network-structured high porosity, and proper N content, most desired as a catalyst support. As-prepared Ru/N-GPC catalyst shows a remarkably low overpotential of 9.6 mV (vs. RHE) at 10 mA/cm2, which is near ideal, providing 12 times faster hydrogen production rate than state-of-the-art Pt/C. We explain the atomistic basis for this low overpotential and superb stability via Grand canonical quantum mechanics calculations. These calculations show that pyrrolic-N in the support strengthens the coupling to the Ru NP while weakening the binding of H to Ru NP to accelerate the Tafel step.

Growth in situ of NiSe2/Ni hybrids in N-doped carbon nanotubes for enhanced overall water splitting

Interface engineering plays an important role to improve the performance of heterostructures. Growth in situ makes the heterostructures with ideal interface natures. Here, the growth in situ of Ni components occurred on N-doping carbon nanotube (Ni-N-CNT) by one-step thermal polymerization for excellent overall water splitting. NiSe2/Ni-N-CNT with well-developed interface was created by selenium treatment of Ni-N-CNT, which improved the carrier transfer efficiency and increased electrochemical active sites. The formation of NiSe2/Ni hybrids improved hydrogen evolution reaction (HER). Ni and Se sites were proved in different electrolytes. The overpotential of NiSe2/Ni-N-CNT at -10 mA·cm−2 was 196 and 220 mV, and Tafel slope is 52 and 70 mV/dec in acidic and alkaline solutions, respectively. NiSe2/Ni-N-CNT revealed well kinetic effect compared with other control samples both in HER and oxygen evolution reaction (OER). The voltage of the electrolytic cell with NiSe2/Ni-N-CNT||NiSe2/Ni-N-CNT electrode was 1.757 and 1.954 V at 10 and 40 mA·cm−2, respectively. NiSe2/Ni-N-CNT as an electrolytic cell electrode was stable for efficient overall water splitting after 9.5 h. The formation of NiSe2/Ni-N-CNT heterostructures supplied a utilizable approach for improving HER and OER to get highly efficient catalysts.