Remarkable Hydrogen Evolution Reaction Performance Research Articles

Honeycomb-structured S and N-codoped highly graphitized carbon as a catalyst support for Rh nanoparticles: A new benchmark electrocatalyst for hydrogen evolution reaction

State-of-the-art electrocatalysts are based on catalytically active metal deposited on conductive porous carbon. Herein, we report a new strategy of engineering of a honeycomb-structured S and N dual-doped graphene-like carbon (SNG) as a supporting material for Rh catalysts by a simple low-temperature (850 °C) pyrolysis of S-doped carbon nitride (S-CN) in the presence of Mg. Interestingly, here Mg plays a marvelous dual role not only as a reducing agent for graphitizing the S-CN but also as a precursor for new Mg3N2 and MgS products, which play as pore-generating templates for honeycomb-like structures. This features highly robust graphitized carbon with excellent electrical conductivity, proper S and N content, and porosity, making it highly desirable as catalyst support. Supporting Rh (5.2 wt.%) on SNG outperforms state-of-the-art commercial Pt/C electrodes for hydrogen evolution reaction (HER) under alkaline settings (1.0 M KOH) with an extremely lower overpotential of 13 mV at 10 mA cm−2, a lower Tafel value, and a higher turnover frequency. In addition, Rh/SNG as the cathode for industrial water electrolysis in 6.0 M KOH electrolyte at 70 °C shows excellent performance with only 1.76 Vcell to achieve 500 mA cm−2 and maintains long-term durability with negligible decay. The distinctive properties of SNG, including S and N dual doping, high graphiticity, superior electrical conductivity, and honeycomb-like hierarchical meso‑ and macropore structure, are credited with this remarkable HER performance. The S and N dopants in the SNG framework optimize the electronic structure of the Rh by synergistic interaction between them as illustrated by first-principal density functional theory calculations and electronic structure analysis.

Ru Regulated Electronic Structure of PdxCuy Nanosheets for Efficient Hydrogen Evolution Reaction in Wide pH Range.

The development of highly effective catalysts for hydrogen evolution reaction (HER) in a wide pH range is crucial for the sustainable utilization of green energy utilization, while the slow kinetic reaction rate severely hinders the progress of HER. Herein, the reaction kinetic issue is solved by adjusting the electronic structure of the Ru/PdxCuy catalysts. The champion catalyst displays a remarkable performance for HER with the ultralow overpotential (27, 28, and 97mV) in 1.0m KOH, 0.5m H2SO4, and 1.0m PBS at 10mA cm-2 and high the mass activity (3036 A g-1), respectively, superior to those of commercial Pt/C benchmarks and most of reported electrocatalysts, mainly due to its low reaction activation energy. Density functional theory (DFT) calculations indicate that Ru doping contributes an electron-deficient 3d band, which promotes water adsorption. Additionally, this also leads to an upward shift of the d-band center of Pd and a downward shift of the d-band center of Cu, further optimizing the adsorption/dissociation of H2O and H*. Results from this work may provide an insight into the design and synthesis of high-performance pH-universal HER electrocatalysts.

Durable Pulse-Electrodeposited Ni-Fe-S Nanosheets Supported on a Ni-S Three Dimensional Pattern as Robust Bifunctional Electrocatalysts for Hydrogen Evolution and Urea Oxidation Reactions.

This study aims to establish easy-to-fabricate and novel structures for the synthesis of highly active and enduring electrocatalysts for the hydrogen evolution reaction (HER) and urea oxidation reaction (UOR). Gradient electrodeposition and four different time regimes were utilized to synthesize Ni-S 3D patterns with the optimization of electrodeposition time. Pulse electrodeposition was employed for the synthesis of Ni-Fe-S nanosheets at three different frequencies and duty cycles to optimize the pulse electrodeposition parameters. The sample synthesized at 13 min of gradient electrodeposition with a 1 Hz frequency and 0.7 duty cycle for pulse electrodeposition demonstrated the best electrocatalytic performance. The optimized electrode further showed remarkable performance for HER and UOR reactions, requiring only 54 mV and 1.25 V to deliver 10 mA cm-2 for HER and UOR, respectively. Moreover, the overall cell voltage of the two-electrode system in 1 M KOH and 0.5 M urea was measured at 1.313 V, delivering 10 mA cm-2. Constructing Ni-Fe-S nanosheets on 3D Ni-S significantly increased the electrochemical surface area from 51 to 278 for the Ni-S and Ni-Fe-S layers. Tafel slopes were measured as 138 and 182 mV dec-1 for the HER and UOR for the Ni-S coating layer and 97 mV dec-1 for the HER and 131 mV dec-1 for the UOR for the optimal Ni-Fe-S nanosheets on Ni-S. Minimal changes in the potential were observed at 100 mA cm-2 in 50 h regarding the HER and UOR, signifying exceptional electrocatalytic stability. This study provides economically viable, highly active, and long-lasting electrocatalysts suitable for HER and UOR applications.

Acenaphthenediimine complex-bridged porphyrin porous organic polymer with enriched active sites as a robust water splitting electrocatalyst

To realize efficient water splitting, a highly promising hydrogen evolution reaction (HER) electrocatalyst is needed for the generation of hydrogen. Herein, we demonstrate a novel acenaphthenediimine complex-bridged porphyrin porous organic polymer (NiTAPP-NiACQ) with enriched active metal sites and hierarchical pores. The as-prepared NiTAPP-NiACQ exhibits good long-term durability and remarkable HER performance in 1.0 M KOH with a low overpotential of 117 mV at 10 mA cm−2, which is comparable to many previously reported electrocatalytic HER systems. Furthermore, a simple water-alkali electrolyzer using NiTAPP-NiACQ as the cathode requires a small cell voltage of 1.59 V to deliver a current density of 10 mA cm−2 at room temperature, along with outstanding durability. NiTAPP-NiACQ features not only a metal ion as the catalytic active center in the porphyrin core but also metal ion coordination on the anthraquinone component to promote HER performance, enabling multiple metal ions as the electrocatalytic active sites for the HER reaction. The excellent HER activity of NiTAPP-NiACQ is ascribed to a combination of mechanisms. These findings highlight the viability of porphyrin-derived porous organic polymers in energy conversion processes.

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.

Constructing Heterogeneous Interface by Growth of Carbon Nanotubes on the Surface of MoB2 for Boosting Hydrogen Evolution Reaction in a Wide pH Range.

Transition metal diborides represented by MoB2 have attracted widespread attention for their excellent acidic hydrogen evolution reaction (HER). Nevertheless, their electrocatalytic performance is generally unsatisfactory in high-pH electrolytes. Heterogeneous interface engineering is one of the most promising methods for optimizing the composition and structure of electrocatalysts, thereby greatly affecting their electrochemical performance. Herein, a heterostructure, composed of MoB2 and carbon nanotubes (CNTs), is rationally constructed by boronizing precursors including (NH4 )4 [NiH6 Mo6 O24 ]·5H2 O (NiMo6 ) and Co complexes on the carbon cloth (Co,Ni-MoB2 @CNT/CC). In this method, NiMo6 is boronized to form MoB2 by a modified molten-salt-assisted borothermal reduction. Meanwhile, Co catalyzes extra carbon sources to grow CNTs on the surface of MoB2 . Thanks to the successful production of the heterostructure, Co,Ni-MoB2 @CNT/CC exhibits remarkable HER performance with a low overpotential of 98.6, 113.0, and 73.9mV at 10mAcm-2 in acidic, neutral, and alkaline electrolytes, respectively. Notably, even at 500mAcm-2 , the electrochemical activity of Co,Ni-MoB2 @CNT/CC exceeds that of Pt/C/CC in an alkaline solution and maintains over 50h. Theoretical calculations reveal that the construction of theheterostructure is beneficial to both water dissociation and reactive intermediate adsorption, resulting in superior alkaline HER performance.

VFe@Ni/Ni3N Mott-Schottky heterojunction induced electronic modulation for efficient alkaline water splitting

Designing affordable and productive bifunctional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has been a long-term goal of anion exchange membrane water electrolysis (AEMWE). Heteroatoms doping and heterostructure construction are generally considered as effective methods for electrocatalysts modification. Herein, V and Fe co-doped Ni/Ni3N (VFe@Ni/Ni3N) electrocatalyst with a Mott-Schottky heterostructure was prepared by hydrothermal and NH3 reduction methods. The formation of Ni/Ni3N Mott-Schottky heterojunction can effectively trigger the self-driven carrier transfer on the heterointerfaces, thus accelerating charges achievement to the surface active sites and advancing the catalytic efficiency. Meanwhile, the co-doping of V and Fe lowers the flat-band potential of Ni/Ni3N, leading to greater electron density, which increases the electron transport potentiality and facilitates the adsorption and reduction of H* in the HER process. Therefore, a remarkable performance for HER with overpotentials of 47 and 180 mV at 10 and 200 mA cm−2 in alkaline solution was achieved. Significant progress has also been made in OER and the full water electrolysis. Furthermore, for the AEMWE with VFe@Ni/Ni3N, a low applied cell voltage of only 1.75 V was needed to reach a high current density of 600 mA cm−2 with an impressive long-term stability of 100 h. This study supplies an innovative strategy of electronic modulation by co-doping and Mott-Schottky heterojunction construction, which is referential for the advancement of economic electrocatalysts for sustainable energy systems.

Metallic W/WO2 solid-acid catalyst boosts hydrogen evolution reaction in alkaline electrolyte

The lack of available protons severely lowers the activity of alkaline hydrogen evolution reaction process than that in acids, which can be efficiently accelerated by tuning the coverage and chemical environment of protons on catalyst surface. However, the cycling of active sites by proton transfer is largely dependent on the utilization of noble metal catalysts because of the appealing electronic interaction between noble metal atoms and protons. Herein, an all-non-noble W/WO2 metallic heterostructure serving as an efficient solid-acid catalyst exhibits remarkable hydrogen evolution reaction performance with an ultra-low overpotential of −35 mV at −10 mA/cm2 and a small Tafel slope (−34 mV/dec), as well as long-term durability of hydrogen production (>50 h) at current densities of −10 and −50 mA/cm2 in alkaline electrolyte. Multiple in situ and ex situ spectroscopy characterizations combining with first-principle density functional theory calculations discover that a dynamic proton-concentrated surface can be constructed on W/WO2 solid-acid catalyst under ultra-low overpotentials, which enables W/WO2 catalyzing alkaline hydrogen production to follow a kinetically fast Volmer-Tafel pathway with two neighboring protons recombining into a hydrogen molecule. Our strategy of solid-acid catalyst and utilization of multiple spectroscopy characterizations may provide an interesting route for designing advanced all-non-noble catalytic system towards boosting hydrogen evolution reaction performance in alkaline electrolyte.

Scalable Synthesis of 2D Mo2 C and Thickness-Dependent Hydrogen Evolution on Its Basal Plane and Edges.

2D transition metal carbides (2D TMCs and MXenes) are promising candidates for applications of energy storage and catalysis. However, producing high-quality, large 2D flakes of Mo2C MXene has been challenging. Here, a new salt-assisted templating approach is reported that enables the direct synthesis of 2D Mo2 C with low defect concentrations. KCl acts as a template to form an intermediate 2D product, facilitating Mo2 C formation without coarsening upon melting. The thickness of the flakes produced can range from monolayer (0.36 nm) to 10 layers (4.55 nm), and the electrocatalytical hydrogen evolution reaction (HER) activity of 2D Mo2 C is inversely proportional to its thickness. The monolayer Mo2 C shows remarkable HER performance with a current density of ≈6800 mA cm- 2 at 470 mV versus reversible hydrogen electrode and an ultrahigh turnover frequency of ≈17 500 s- 1 . This salt-assisted synthesis approach can also produce WC and V8 C7 nanosheets, expanding the family of 2D carbides. The new pathway eliminates the need for layered ceramic precursors, making it a versatile approach to direct synthesis of MXene-like 2D carbides.

Engineering Amorphous/Crystalline Ru(OH)3/CoFe-Layered Double Hydroxide for Hydrogen Evolution at 1000 mA cm-2.

For large-scale industrial applications, it is highly desirable to create effective, economical electrocatalysts with long-term stability for the hydrogen evolution reaction (HER) at a large current density. Herein, we report a unique motif with crystalline CoFe-layered hydroxide (CoFe-LDH) nanosheets enclosed by amorphous ruthenium hydroxide (a-Ru(OH)3/CoFe-LDH) to realize the efficient hydrogen production at 1000 mA cm-2, with a low overpotential of 178 mV in alkaline media. During the continuous HER process for 40 h at such a large current density, the potential remains almost constant with only slight fluctuations, indicating good long-term stability. The remarkable HER performance can be attributed to the charge redistribution caused by abundant oxygen vacancies in a-Ru(OH)3/CoFe-LDH. The increased electron density of states lowers the charge-transfer resistance and promotes the formation and release of H2 molecules. The water-splitting electrolyzer with a-Ru(OH)3/CoFe-LDH as both an anode and a cathode in 1.0 M KOH demonstrates stable hydrogen production and a 100% faradic efficiency. The design strategy of interface engineering in this work will inspire the design of practical electrocatalysts for water splitting on an industrial scale.

Electronic Modulation of Metal-Organic Frameworks Caused by Atomically Dispersed Ru for Efficient Hydrogen Evolution.

Designing excellent electrocatalysts for the hydrogen evolution reaction (HER) is extremely significant in producing clean and sustainable hydrogen fuel. Herein, a rational strategy is developed to fabricate a promising electrocatalyst by introducing atomically dispersed Ru into a cobalt-based metal-organic framework (MOF), Co-BPDC (Co(bpdc)(H2 O)2 , BPDC: 4,4'-Biphenyldicarboxylic acid). The obtained CoRu-BPDC nanosheet arrays exhibit remarkable HER performance with an overpotential of 37mV at a current density of 10mAcm-2 in alkaline media, which is superior to most of the MOF-based electrocatalysts and comparable to the commercial Pt/C. Synchrotron radiation-based X-ray absorption fine structure (XAFS) spectroscopy studies verify that the isolated Ru atoms are dispersed in Co-BPDC nanosheets with the formation of five-coordinated Ru-O5 species. XAFS spectroscopy combined with density functional theory (DFT) calculations unravels that atomically dispersed Ru can modulate the electronic structure of the as-obtained Co-BPDC, contributing to the optimization of binding strength for H* and the enhancement of HER performance. This work opens a new avenue to rationally design highly-active single-atom modified MOF-based HER electrocatalysts via modulating electronic structures of MOF.

Flash joule heating synthesis of carbon supported ultrafine metallic heterostructures for high-performance overall water splitting

Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are pivotal electrochemical reactions in water splitting and require efficient and durable electrocatalysts. Developing carbon-supported ultrafine nanocrystals embracing rich active sites serves an effective strategy to produce efficient electrocatalysts. Herein, we report a facile flash joule heating technology to prepare bifunctional electrocatalyst toward HER and OER, in which ultrafine Cu and Ru metallic heterostructures confined within carbon matrix are directly coated on the conductive carbon cloth (Ru-Cu@CM/CC). Benefiting from the homogeneously dispersed nanoclusters with rich active sites, Ru-Cu@CM/CC shows remarkable performance for HER and OER in both alkaline and acid solution, outperforming Pt/C and RuO2, respectively. Remarkably, the two-electrode electrolyzers using Ru-Cu@CM/CC display low voltages in alkaline and acid electrolyte. The exemplified Ru-Cu@CM/CC illustrates the effectiveness of flash joule heating strategy in preparing metallic heterostructures. The satisfactory electrocatalytic performance also inspires the construction of heterostructures for overall water splitting.

Metal-organic frameworks derived self-supported Ni2P nanorod arrays for electrocatalytic hydrogen evolution

The development of efficient and low-cost electrocatalysts for hydrogen evolution reaction (HER) is of importance. Herein, we demonstrate a self-supported Ni2P nanostructure with nanorod arrays morphology, fabricated by directly growing metal-organic frameworks (MOFs) on the commercial nickel foam prior to phosphorization treatment, as an electrocatalyst for HER. This electrocatalyst exhibits remarkable electrocatalytic HER activity in an alkaline electrolyte, affording current densities of 10 and 100 mA cm−2 at the overpotentials of 120 and 168 mV, respectively, accompanied with a low Tafel slope of 37 mV dec−1. Furthermore, this electrocatalyst shows a current density of 105 mA cm−2, and this current density can be retained for more than 20 h, suggesting its superior stability. This remarkable HER performance is believed a result of superiority for its structural integrality and mechanical stability.

In-Situ and controllable construction of Mo2N embedded Mo2C nanobelts as robust electrocatalyst for superior pH-universal hydrogen evolution reaction

The development of high active and cost-effective transition metal based catalysts as alternatives to Pt-based electrocatalysts for pH-universal hydrogen evolution reaction (HER) is highly desirable. Herein, we proposed a novel strategy to construct Mo2N uniformly embedded Mo2C nanobelt arrays electrocatalyst on N doped carbon framework (Mo2N-Mo2C/NC NBAs) by nitridation of MoOx/C hybrid precursors and subsequent annealing. The effect of N content towards the composition ratio of Mo2N to Mo2C and the structural evolution were studied. The in-situ formed Mo2N reduces the sintering of Mo2C phase and creates amounts of compact Mo2N-Mo2C interfaces and mesopores. Because of these high active interfaces, mesopores structure and self-supported architecture, the resultant Mo2N-Mo2C/NC catalyst exhibits remarkable HER performance and durability over a wide pH range, as exemplified by a small overpotentials of 75, 93, and 114 mV at 10 mA cm−2, and Tafel slopes of 43, 58, and 62 mV dec−1 in the alkaline, neutral and acidic media. The results reveal a new avenue to design highly efficient electrocatalysts with tailored hetero/microstructures, which could be extended to fabricate other high-performance electrocatalyst and electrode materials for electrochemical energy conversion.

Hollow Nanowire Constructed by NiCo Doped RuO2 Nanoparticles for Robust Hydrogen Evolution at High-Current-Density.

Large-current-density electrocatalytic water splitting is essential for industrial hydrogen production, but it is currently hindered by lacking active and robust hydrogen evolution reaction (HER) catalysts. Herein, a novel electrode of hollow nanowire arrays constructed by NiCo modified RuO2 nanoparticles on Ni foam (NiCo@RuO2 HNAs/NF) for high-performance HER was reported. Such efficient electrode was fabricated by ion exchange with NF-supported Ni modified cobalt carbonate hydroxide nanowire arrays template (Ni@CoCH NAs/NF). The formed NiCo@RuO2 HNAs/NF only needed overpotentials of 148.5 and 236.1 mV to deliver 500 and 1000 mA cm-2 , respectively, along with excellent stability at the high-current-density for 300 h. Such remarkable HER performance was mainly attributed to the hollow structure with high surface area, hydrophilic feature, and NiCo@RuO2 with optimized hydrogen evolution kinetics. After coupling with anodic Ni@CoCH NAs/NF, our electrolyzer outperformed Pt/C-IrO2 and most other Ru-based electrolyzers. This work provides a promising Pt alternative catalyst for profitable H2 production.

Synthesis, Physical Properties and Electrocatalytic Performance of Nickel Phosphides for Hydrogen Evolution Reaction of Water Electrolysis.

Nickel phosphides have been investigated as an alternative to noble metals and have emerged as potential catalysts that can efficiently catalyze the hydrogen evolution reaction (HER). However, the impacts of facet morphology and crystal structure of the nickel phosphides on their catalytic reactivity have not been systematically investigated. Herein, nickel phosphides with different crystalline states were prepared through a facile calcination treatment. It was found that the calcination treatment had important effects on the phase compositions, morphologies, and crystallinity of nickel phosphides, which are closely related to their HER activity. Generally, the crystallized Ni-P catalysts exhibited faster kinetics than the amorphous Ni-P. In particular, the Ni-P 300 showed remarkable HER performance with of ca. 65 mV, along with a very low Tafel slope of ca. 44 mV dec−1 due to the increased catalytically active sites. Furthermore, the Ni-P 300 exhibited negligible decay during the 140 h galvanostatic electrolysis, showing better catalytic stability than the commercial Pt/C catalyst. Compared with the amorphous Ni-P, the boosted HER activity of the Ni-P 300 could benefit from the mixed nanocrystalline Ni2P and Ni3P, which could contribute to the Hads adsorption/desorption abilities and helped provide more activity sites, promoting the HER performance.

Facet engineering of NiCo2S4 electrocatalysts for enhanced hydrogen evolution reaction

Crystal facet engineering is considered to be a powerful method to maximize the inherent catalytic properties of electrocatalysts. In this research, polyvinylpyrrolidone (PVP) served as a surfactant to realize the controllable synthesis of sub-microspheres NiCo2S4 with a highly exposed (400) crystal facet. The sub-microspheres NiCo2S4 (P-0.2) shows excellent catalytic activities as a cathode toward hydrogen evolution reaction (HER) with a lower overpotential of 235 mV at 10 mA·cm−2 in alkaline electrolyte. Moreover, the sub-microspheres NiCo2S4 presents satisfactory durability in the alkaline solution for 24 h. Such remarkable HER performance of electrocatalyst is benefited from the unique sub-microspheres structure, which could highly expose specific crystal facets to provide abundant active sites, and thus enhance the mass/electron transfer efficiency. Furthermore, the increased exposure of (400) facet of NiCo2S4 crystal will offer more S2- during HER, it can effectively stabilize the reaction intermediates.

Ru decorated Co nanoparticles supported by N-doped carbon sheet implements Pt-like hydrogen evolution performance in wide pH range

Development of high-performance pH-universal electrocatalyst for hydrogen evolution reaction (HER) is a vital step towards hydrogen economy but remains a major challenge. Herein, the Ru decorated Co nanoparticles supported by N-doped carbon sheets (Ru/Co@NC) are prepared by galvanic exchange reaction and display a remarkable performance for HER. In the 1.0 M KOH, 0.01 M PBS and 0.5 M H2SO4, respectively, Ru/Co@NC shows low overpotentials of 10, 283 and 50 mV at the current density of 10 mA cm−2, comparable to benchmark Pt/C (23, 289 and 37 mV). Furthermore, deep experimental researches and DFT calculations indicate that the Ru-Co heterostructure shows more suitable energy of H2O* dissociation and H* adsorption compared to Ru and Co, which can significantly improve the HER activity. Besides excellent activity, in a wide pH range, the Ru/Co@NC also exhibits good stability with negligible current loss after a long-time HER test (30 h). This work may provide ponderable strategies for developing an efficient pH-universal HER electrocatalyst.

α-MoB2 Nanosheets for Hydrogen Evolution in Alkaline and Acidic Media

α-MoB2 is recognized as the most efficient molybdenum boride for electrocatalytic hydrogen evolution reaction (HER). However, the convenient synthesis of single phase α-MoB2 is still challenging, and its HER activity in alkaline electrolytes remains unclear. Herein, we report the first successful synthesis of the α-MoB2 nanosheets by a simple and facile molten salt method through the MoCl5 and NaBH4 reaction at 850 °C. The α-MoB2 nanosheets exhibit a remarkable HER performance in alkaline electrolytes, delivering a low overpotential of 124 mV at a current density of 10 mA/cm2. In acidic electrolytes, an improved performance was found in comparison to that of the bulk and nano α-MoB2 with an overpotential as low as 141 mV at 10 mA/cm2. Such HER performance arises from the nanosheet structure that allows more active planes to be exposed. In addition, the α-MoB2 nanosheets possess an outstanding stability in both acidic and alkaline media, showing negligible current density drop even after 3000 cycles and more than 24 h of potentiostatic operation.

Facet-Selective hydrogen evolution on Rh2P electrocatalysts in pH-Universal media

Surface atomic structures of transition metal phosphides determine the electrocatalytic activities toward hydrogen evolution reaction (HER). In this work, we developed a new facet-guided phosphorization strategy to synthesize Rh2P electrocatalysts with tunable facet exposure and further unveil their intrinsic facet-dependent HER activity in pH-universal media. The Rh2P nanoparticles feature {111} and {200} facets when the precursors of Rh nanoctahedron and nanocube are used, respectively. The Rh2P{200} catalyst showed a remarkable HER performance with the overpotential of 23, 22 and 54 mV at a current density of 10 mA cm−2 in 1.0 M KOH, 0.5 M H2SO4 and 1.0 M phosphate buffer, respectively. The mass activity and specific activity of Rh2P{200} were 3～5-times higher than those of Rh2P{111} and Pt/C catalysts. As elucidated using theoretical calculations, the overlapping of Rh-4d and P-3p of Rh2P{200} and Rh2P{111} results in distinct electronic states of surface Rh atoms, leading to varied free energies for water dissociation and hydrogen adsorption/desorption.