Structural specificity of the kinetics of the hydrogen evolution reaction on the low-index surfaces of Pt single-crystal electrodes in 0.5 M dm−3 NaOH

Reactivity of Resorcinol on Pt(511) Single-Crystal Surface and Its Effect on the Kinetics of Underpotentially Deposited Hydrogen and Hydrogen Evolution Reaction in 0.1 M NaOH Electrolyte

This article presents cyclic voltammetry, Tafel polarization, and ac. impedance spectroscopy examinations of resorcinol (RC) ion reactivity on Pt(511) single-crystal plane and the effect of surface-electrosorbed RC ions on the kinetics of UPD H (underpotentially deposited hydrogen) and HER (hydrogen evolution reaction) processes in 0.1 M NaOH solution. Obtained data delivered a proof for the RC ion surface adsorption and its later electroreduction over the potential range characteristic for the UPD H. A favourable role of platinum-adsorbed resorcinol anions on the kinetics of the UPD H and HER processes is also discussed. The above was explained via the recorded capacitance and charge-transfer resistance parameters (the presence of resorcinol at 1.5 × 10-3 M in 0.1 M NaOH caused significant reduction in the resistance parameter values by 3.9 and 2.6 times, correspondingly, for the UPD of H at 50 mV and the HER process, examined at -50 mV vs. RHE) along with the charge transients, produced by injecting small amounts of RC-based 0.1 M NaOH solution to initially RC-free base electrolyte on the Pt(511) electrode plane (a large cathodic charge-transient density of -90 µC cm-2 was recorded at the electrode potential of 50 mV).

Multidimensional Electrochemistry Decodes the Operando Mechanism of Hydrogen Oxidation

Being an efficient approach to the utilization of hydrogen energy, the hydrogen oxidation reaction (HOR) is of particular significance in the current carbon-neutrality time. Yet the mechanistic picture of the HOR is still blurred, mostly because the elemental steps of this reaction are rapid and highly entangled, especially when deviating from the thermodynamic equilibrium state. Here we report a strategy for decoding the HOR mechanism under operando conditions. In addition to the wide-potential-range I-V curves obtained using gas diffusion electrodes, we have applied the AC impedance spectroscopy to provide independent and complementary kinetic information. Combining multidimensional data sources has enabled us to fit, in mathematical rigor, the core kinetic parameter set in a 5-D data space. The reaction rate of the three elemental steps (Tafel, Heyrovsky, and Volmer reactions), as a function of the overpotential, can thus be distilled individually. Such an undocumented kinetic picture unravels, in detail, how the HOR is controlled by the elemental steps on polarization. For instance, at low polarization region, the Heyrovsky reaction is relatively slow and can be ignored; but at high polarization region, the Heyrovsky reaction will surpass the Tafel reaction. Additionally, the Volmer reaction has been the fastest within overpotentials of interest. Our findings not only offer a better understanding of the HOR mechanism, but also lay the foundation for the development of improved hydrogen energy utilization systems.

Recent Tendency on Transition-Metal Phosphide Electrocatalysts for the Hydrogen Evolution Reaction in Alkaline Media

Hydrogen energy is regarded as an auspicious future substitute to replace fossil fuels, due to its environmentally friendly characteristics and high energy density. In the pursuit of clean hydrogen production, there has been a significant focus on the advancement of effective electrocatalysts for the process of water splitting. Although noble metals like Pt, Ru, Pd and Ir are superb electrocatalysts for the hydrogen evolution reaction (HER), they have limitations for large-scale applications, mainly high cost and low abundance. As a result, non-precious transition metals have emerged as promising candidates to replace their more expensive counterparts in various applications. This review focuses on recently developed transition metal phosphides (TMPs) electrocatalysts for the HER in alkaline media due to the cooperative effect between the phosphorus and transition metals. Finally, we discuss the challenges of TMPs for HER.

Electrochemical hydrogen evolution on Pt-based catalysts from a theoretical perspective

Hydrogen evolution reaction (HER) by splitting water is a key technology toward a clean energy society, where Pt-based catalysts were long known to have the highest activity under acidic electrochemical conditions but suffer from high cost and poor stability. Here, we overview the current status of Pt-catalyzed HER from a theoretical perspective, focusing on the methodology development of electrochemistry simulation, catalytic mechanism, and catalyst stability. Recent developments in theoretical methods for studying electrochemistry are introduced, elaborating on how they describe solid-liquid interface reactions under electrochemical potentials. The HER mechanism, the reaction kinetics, and the reaction sites on Pt are then summarized, which provides an atomic-level picture of Pt catalyst surface dynamics under reaction conditions. Finally, state-of-the-art experimental solutions to improve catalyst stability are also introduced, which illustrates the significance of fundamental understandings in the new catalyst design.

Ultralong-lifetime Ti/RuO2-IrO2@Pt anodes with a strong metal-support interaction for efficient electrochemical mineralization of perfluorooctanoic acid

Electrocatalytic oxidation is regarded as an effective technique for decomposing refractory organic compounds like perfluorooctanoic acid (PFOA). However, achieving highly efficient and long-life electrodes is still a great challenge. Herein, Ti/RuO₂-IrO₂@Pt anodes consisting of Pt⁴⁺ and Pt⁰ species were fabricated by combining modified microemulsion technology with a calcination process, in which Pt nanoparticles were highly dispersed and encapsulated in Ru-Ir composite oxides to form a strong metal-support interaction (SMSI) structure. The as-constructed SMSI layer on the Ti/RuO₂-IrO₂@Pt anode resulted in the improvement of the charge transfer capability and also increased the degradation (99.30%) and mineralization (91.32%) of PFOA during the electrochemical oxidation process. Notably, the service lifetime of Ti/RuO₂-IrO₂@Pt anodes was remarkably improved from 24 to 42.3 h compared to commercial Ti/RuO₂-IrO₂ anodes. Moreover, the possible degradation mechanism of PFOA was also speculated through the detection of short-chain perfluorocarboxylic acids and reactive radicals. These results not only revealed that the concept and methodology of SMSI could be an effective way for constructing highly efficient and stable electrocatalysts but also greatly advanced fundamental understanding.

On the thermodynamics of hydrogen adsorption over Pt(111) in 0.05M NaOH

The reasons for the sluggish kinetics of the hydrogen adsorption reaction in alkaline media remain a question still to be solved. This information is important to achieve a complete understanding of the mechanistic details that could lead to the production of key catalytic materials necessary for the development of a future hydrogen economy. For a better understanding of this reaction, it is important to acquire information about the thermodynamic parameters characteristic of the different steps in the reaction. Among these, the hydrogen adsorption is a key step in the process of hydrogen evolution. Although some debate still remains about the difference between adsorbed hydrogen in the underpotential deposition (UPD) region and at the overpotential deposition region, there is no doubt that understanding the former can help in the understanding of the latter. Making use of charge density measurements, we report on this paper a thermodynamic study of the hydrogen UPD process on Pt(111) in 0.05M NaOH over the range of temperatures from 283 ≤ T/K ≤ 313. The coulometric features corresponding to H_UPD allow for the calculation of the hydrogen coverage and a fit to a Generalized Frumkin isotherm. From these values, different thermodynamic functions for the UPD reaction have been calculated: ΔG_ads, ΔS_ads, ΔH_ads, and the Pt-H bond energy. From extrapolation, a value of ΔS_ads ^◦=-7.5±4Jmol^-1K^-1 was found, which is very close to 0, much lower than previously reported measurements both in acid and in alkaline solutions. Such value has an effect on the enthalpy and bond energy calculations, the latter having a decreasing tendency with pH and coverage. This tendency is completely different from the acidic systems and implies that the change in the thermodynamic functions due to the formation of the double layer and the reorganization of interfacial water has a strong influence on the process in high pH solutions.

Strain in a platinum plate induced by an ultrahigh energy laser boosts the hydrogen evolution reaction

The ligand and the strain near the active sites in catalysts jointly affect the electrocatalytic activity for the catalytic industry. In many cases, there is no effective strategy for the independent study of the strain effect without the ligand effect on the electrocatalytic activity for the hydrogen evolution reaction (HER). Laser shock peening (LSP) with a GW cm-2 level power density and a 10-30 ns short pulse is employed to form compressive strain on the surface and in the depth direction of a platinum (Pt) plate, which changes the inherent interatomic distance and modifies the energy level of the bonded electrons, thereby greatly optimizing the energy barrier for the HER. The crystal lattice near the surface of the LSP Pt plate is distorted by the strain, and the interplanar spacing decreases from 0.225 nm in the undeformed region to 0.211 nm in the deformed region. The specific activity of the LSP Pt has an increase of 2.9 and 6.4 times in comparison with that of the pristine Pt in alkaline and acidic environments, respectively. This investigation provides a novel strategy for the independent study of the strain effect on the electrocatalytic activity and the improvement of electrocatalysts with high performance in extensive energy conversion.

Facile Atomic-Level Tuning of Reactive Metal-Support Interactions in the Pt QDs@ HF-Free MXene Heterostructure for Accelerating pH-Universal Hydrogen Evolution Reaction

Supported metallic nanoparticles render highly tunable physical and chemical properties to mixed-dimensionality materials in electrocatalysts. However, some supports are susceptible to being dissolved in acidic solution or are unstable in ambient air. The development of high-performance catalysts has been facing the major hurdles of the sluggish activity in alkaline solution and requesting high energy to stabilize the nanoparticles on their supports, challenging the pH-universality and the applicability of the supported metallic nanoparticles. Here, a one-step strategy is proposed to modulate the growth of Pt quantum dots (QDs) on HF-free MXene under atomic-level by a low-temperature metal-support interaction reaction. By controllable tailoring in the morphology and strain induced by terminations, Pt (111) QDs with a sub-nanoscale size of 1.15 nm are grown as 0D/1D heterostructure to overcome the restrictions of employing reduction gas and high annealing temperature. The catalyst exhibits a low overpotential of 33.3 mV for acidic solution, while 65.1 mV for alkaline solution at a specific current density of 10 mA cm-2 . This study not only paves a scalable pathway to developing cost-efficient catalysts in moderate conditions, but also demonstrates an effective surface modulation strategy for 0D/1D heterostructures.

NH2-MIL-125(Ti) doped CdS/Graphene composite as electro and photo catalyst in basic medium under light irradiation

The development of active electrocatalysts and photocatalysts for hydrogen evolution reaction (HER) and for environmental remediation is a huge challenge. Research is still underway on the development of low-cost catalytic materials with appreciable efficiency for HER. In the present study, a composite of metal organic framework (MOF) with CdS and graphene (NH₂-MIL-125(Ti)/CdS-graphene) composites were developed with different loadings of graphene material via solvothermal technique. Further the electrocatalytic activity of the synthesized catalysts were investigated for HER and photocatalytic degradation of dye. Results show that the synthesized catalyst with a less amount of graphene was more active. HER results showed a less Tafel slope of 70.8 and 61.9 mVdec^-1 with 15.6 mA/cm² and 15.46 mA/cm² current densities under light on and off conditions. Further the dye degradation activity of the synthesized catalysts was tested with Rhodamine B dye and results showed that the catalyst showed excellent activity for low weight loading of graphene with a degradation efficiency of 95 % and followed pseudo first order kinetic model. Overall results showed that the synthesized composites are promising for HER and photocatalytic applications.

The Interrelated Effect of Cations and Electrolyte pH on the Hydrogen Evolution Reaction on Gold Electrodes in Alkaline Media

In this work we study the role of alkali metal cation concentration and electrolyte pH in altering the kinetics of the hydrogen evolution reaction (HER) at gold (Au) electrodes. We show that at moderately alkaline pH (pH 11), increasing the cation concentration significantly enhances the HER activity on Au electrodes (with a reaction order ≈0.5). Based on these results we suggest that cations play a central role in stabilizing the transition state of the rate-determining Volmer step by favorably interacting with the dissociating water molecule (*H-OH^δ- -cat⁺ ). Moreover, we show that increasing electrolyte pH (pH 10 to pH 13) tunes the local field strength, which in turn indirectly enhances the activity of HER by tuning the near-surface cation concentration. Interestingly, a too high near-surface cation concentration (at high pH and high cation concentration) leads to a lowering of the HER activity, which we ascribe to a blockage of the surface by near-surface cations.

Activation Energy of Hydrogen Adsorption on Pt(111) in Alkaline Media: An Impedance Spectroscopy Study at Variable Temperatures

The hydrogen evolution reaction is one of the most studied processes in electrochemistry, and platinum is by far the best catalyst for this reaction. Despite the importance of this reaction on platinum, detailed and accurate kinetic measurements of the steps that lead to the main reaction are still lacking, particularly because of the fast rate of the reaction. Hydrogen adsorption on Pt(111) has been taken as a benchmark system in a large number of computational studies, but reliable experimental data to compare with the computational studies is very scarce. To gain further knowledge on this matter, a temperature study of the hydrogen adsorption reaction has been carried out to obtain kinetic information for this process on Pt(111) in alkaline solution. This was achieved by measuring electrochemical impedance spectra and cyclic voltammograms in the range of 278 ≤ T ≤ 318 (K) to obtain the corresponding surface coverage by adsorbed species and the faradaic charge transfer resistance. From this data, the standard rate constant has been extracted with a kinetic model assuming a Frumkin-type isotherm, resulting in values of 2.60 × 10^-7 ≤ k⁰ ≤ 1.68 × 10^-6 (s^-1). The Arrehnius plot gives an activation energy of 32 kJ mol^-1. Comparisons are made with values calculated by computational methods and reported values for the overall HER, giving a reference frame to support future studies on hydrogen catalysis.

Platinum-Nickel Nanowires with Improved Hydrogen Evolution Performance in Anion Exchange Membrane-Based Electrolysis

Platinum-nickel (Pt-Ni) nanowires were developed as hydrogen evolving catalysts for anion exchange membrane electrolyzers. Following synthesis by galvanic displacement, the nanowires had Pt surface areas of 90 m2 gPt-1. The nanowire specific exchange current densities were 2-3 times greater than commercial nanoparticles and may benefit from the extended nanostructure morphology that avoids fringe facets and produces higher quantities of Pt{100}. Hydrogen annealing was used to alloy Pt and Ni zones and compress the Pt lattice. Following annealing, the nanowire activity improved to 4 times greater than the as-synthesized wires and 10 times greater than Pt nanoparticles. Density functional theory calculations were performed to investigate the influence of lattice compression and exposed facet on the water-splitting reaction; it was found that at a lattice of 3.77 Å, the (100) facet of a Pt-skin grown on Ni3Pt weakens hydrogen binding and lowers the barrier to water-splitting as compared to pure Pt(100). Moreover, the activation energy of water-splitting on the (100) facet of a Pt-skin grown on Ni3Pt is particularly advantageous at 0.66 eV as compared to the considerably higher 0.90 eV required on (111) surfaces of pure Pt or Pt-skin grown on Ni3Pt. This favorable effect may be slightly mitigated during further optimization procedures such as acid leaching near-surface Ni, necessary to incorporate the nanowires into electrolyzer membrane electrode assemblies. Exposure to acid resulted in slight dealloying and Pt lattice expansion, which reduced half-cell activity, but exposed Pt surfaces and improved single-cell performance. Membrane electrode assembly performance was kinetically 1-2 orders of magnitude greater than Ni and slightly better than Pt nanoparticles while at one tenth the Pt loading. These electrocatalysts potentially exploit the highly active {100} facets and provide an ultralow Pt group metal option that can enable anion exchange membrane electrolysis, bridging the gap to proton exchange membrane-based systems.

A Detrimental Effect of Acetonitrile on the Kinetics of Underpotentially Deposited Hydrogen and Hydrogen Evolution Reaction, Examined on Pt Electrode in H2SO4 and NaOH Solutions

The present paper reports AC impedance spectroscopic/Tafel polarization and cyclic voltammetry study on the influence of acetonitrile concentration on the kinetics of UPD of H (underpotential deposition of hydrogen) and HER (hydrogen evolution reaction), examined on polycrystalline and polyoriented single-crystal sphere Pt electrode surfaces in 0.5 M H2SO4 and 0.1 M NaOH supporting solutions. The resulted data provided confirmation of the destructive role of Pt surface-electrosorbed acetonitrile on the kinetics of underpotentially deposited hydrogen, as well as cathodic hydrogen evolution reaction. The above was exclusively elucidated through evaluation of the associated charge-transfer resistance and capacitance (and complementary exchange current-density and Tafel slope) parameters, derived comparatively on Pt for pure and acetonitrile-modified acidic and alkaline electrolytes.

Efficient Energy Conversion and Storage Based on Robust Fluoride-Free Self-Assembled 1D Niobium Carbide in 3D Nanowire Network

Owing to their high robustness and conductivity, 2D transition metal carbides and nitrides known as MXenes are considered as a promising material class for electrochemical catalysis, energy conversion, and storage applications. Nevertheless, conventional hazardous fluoride-based synthesis routes and the intense intralayer bonding restrict the development of MXenes. Herein, a fluoride-free, facile, and rapid method for synthesizing self-assembled 1D architecture from an MXene-based compound is reported. The MXene nanowire (NW) not only provides a robust connection to the flexible substrate but also effectively increases the electrochemically active surface area. The kinetics-favorable structure yields a boosted performance for the hydrogen/oxygen evolution reaction and the intake of the zinc ion. The 1D NW based on MXene compound maintains high stability in a quite low overpotential of 236 mV for 24 h without detachment from the substrate and manifests an exceptional high-power density of 420 W kg-1 over 150 cycles as a flexible aqueous zinc ion battery. This work paves a novel and non-toxic synthesis method for the 1D nanofiber structure from MXene composition and demonstrates its multifunctional applications for energy conversion and storage.

Enhancing the Hydrogen Evolution Reaction Activity of Platinum Electrodes in Alkaline Media Using Nickel-Iron Clusters

Herein, we demonstrate an easy way to improve the hydrogen evolution reaction (HER) activity of Pt electrodes in alkaline media by introducing Ni-Fe clusters. As a result, the overpotential needed to achieve a current density of 10 mA cm^-2 in H₂ -saturated 0.1 m KOH is reduced for the model single-crystal electrodes down to about 70 mV. To our knowledge, these modified electrodes outperform any other reported electrocatalysts tested under similar conditions. Moreover, the influence of 1) Ni to Fe ratio, 2) cluster coverage, and 3) the nature of the alkali-metal cations present in the electrolyte on the HER activity has been investigated. The observed catalytic performance likely originates from both the improved water dissociation at the Ni-Fe clusters and the subsequent optimal hydrogen adsorption and recombination at Pt atoms present at the Ni-Fe/Pt boundary.

Highly efficient electrocatalytic hydrogen evolution promoted by O-Mo-C interfaces of ultrafine β-Mo2C nanostructures

Optimizing interfacial contacts and thus electron transfer phenomena in heterogeneous electrocatalysts is an effective approach for enhancing electrocatalytic performance. Herein, we successfully synthesized ultrafine β-Mo2C nanoparticles confined within hollow capsules of nitrogen-doped porous carbon (β-Mo2C@NPCC) and found that the surface layer of molybdenum atoms was further oxidized to a single Mo-O surface layer, thus producing intimate O-Mo-C interfaces. An arsenal of complementary technologies, including XPS, atomic-resolution HAADF-STEM, and XAS analysis clearly reveals the existence of O-Mo-C interfaces for these surface-engineered ultrafine nanostructures. The β-Mo2C@NPCC electrocatalyst exhibited excellent electrocatalytic activity for the hydrogen evolution reaction (HER) in water. Theoretical studies indicate that the highly accessible ultrathin O-Mo-C interfaces serving as the active sites are crucial to the HER performance and underpinned the outstanding electrocatalytic performance of β-Mo2C@NPCC. This proof-of-concept study opens a new avenue for the fabrication of highly efficient catalysts for HER and other applications, whilst further demonstrating the importance of exposed interfaces and interfacial contacts in efficient electrocatalysis.

Enhancing the Understanding of Hydrogen Evolution and Oxidation Reactions on Pt(111) through Ab Initio Simulation of Electrode/Electrolyte Kinetics

The hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) play an important role in hydrogen-based energy conversion. However, the sluggish kinetics in alkaline media has raised debates on the relevant mechanism, especially on the role of surface hydroxyl (OH*). With the potential-related free energy profiles obtained with density functional theory calculations, the full pH range transient kinetics simulation of HER/HOR polarization curves on Pt(111) agrees well with experimental observations. Studying model systems with varying metal-OH* binding energies confirms that the current near the HOR onset potential is contributed from the pathway through OH^- rather than OH*, suggesting that OH* is unlikely an effective activity descriptor for HOR. The degree of rate control analyses reveal that, while acidic current is controlled solely by the Tafel step, alkaline current is controlled jointly by Tafel and Volmer steps, as the Volmer barrier is considerably increased in alkaline conditions. Finally, based on a model study, we draw up a scheme of reducing the overpotential of alkaline HER/HOR by accelerating the Tafel step.

Theoretical investigation on the hydrogen evolution reaction mechanism at MoS2 heterostructures: the essential role of the 1T/2H phase interface

DFT calculations have been performed to study the HER mechanism at 1T/2H MoS₂ heterostructures. The HER activity along the 1T/2H phase interface is comparable with those at the Mo-edge of 2H MoS₂ and the basal plane of 1T MoS₂.

In Situ Dynamic Nanostructuring of the Cu-Ti Catalyst-Support System Promotes Hydrogen Evolution under Alkaline Conditions

We report an interesting case of in situ dynamic nanostructuring of catalyst and support under hydrogen evolution conditions in basic media. When solution-grown CuO nanoplates on titanium substrates are subjected to hydrogen evolution reaction, besides the reduction of CuO to metallic Cu nanoplates, both catalyst and support simultaneously undergo a nanostructuring process. The process is driven by the dissolution-redeposition of Cu and the alkaline etching of the titanium support. The morphology of the resulting nanocomposite material consists of a porous matrix made of ultrasmall Cu nanocrystals and amorphous TiO _x nanoparticles. Interestingly, the nanostructuring of the catalyst can be finely controlled by varying the applied potential. Such a process leads to a 5.4-fold improvement in the catalyst activity, which is attributed not only to its large active surface area (formed upon nanostructuring), but also to an improved water dissociation activity, provided by the in situ formation of TiO _x nanoparticles. The final catalyst exhibits -10 mA/cm² of current density at a small overpotential of -108 mV and a long-term operational stability up to 50 h. Density functional theory calculations show that the co-presence of Cu and TiO₂ nanoparticles optimizes the free energy of hydrogen adsorption in the final catalyst. Our work highlights the importance of studying the dynamic evolution of catalysts under operational conditions and choice of proper support that enhances the catalyst activity.

Pt and Pt-Ni(OH)2 Electrodes for the Hydrogen Evolution Reaction in Alkaline Electrolytes and Their Nanoscaled Electrocatalysts

The design and synthesis of Pt-based electrocatalysts for the hydrogen evolution reaction (HER) are of great importance for the successful development of hydrogen-based alternative energy technologies. Although Pt is considered to be the most active catalyst for the HER, its reaction performance is limited in alkaline solutions owing to a slow rate for water dissociation. Therefore, many research groups have intensively investigated reaction mechanisms and developed system designs and efficient Pt-based catalysts to enhance the alkaline HER. Herein, we summarize the catalytic surface specificity of Pt and Pt-Ni(OH)₂ materials to control the kinetics of the alkaline HER. In particular, we increase our understanding of Ni(OH)₂ -modified Pt surfaces and the corresponding nanoscaled Pt-Ni(OH)₂ electrocatalysts to improve the sluggish water-dissociation step, and this knowledge will guide us to future sustainable energy applications of advanced nanomaterials.

General Synthetic Strategy for Libraries of Supported Multicomponent Metal Nanoparticles

Nanoparticles comprising three or more different metals are challenging to prepare. General methods that tackle this challenge are highly sought after as multicomponent metal nanoparticles display favorable properties in applications such as catalysis, biomedicine, and imaging. Herein, we report a practical and versatile approach for the synthesis of nanoparticles composed of up to four different metals. This method relies on the thermal decomposition of nanostructured composite materials assembled from platinum nanoparticles, a metal-organic framework (ZIF-8), and a tannic acid coordination polymer. The controlled integration of multiple metal cations (Ni, Co, Cu, Mn, Fe, and/or Tb) into the tannic acid shell of the precursor material dictates the composition of the final multicomponent metal nanoparticles. Upon thermolysis, the platinum nanoparticles seed the growth of the multicomponent metal nanoparticles via coalescence with the metallic constituents of the tannic acid coordination polymer. The nanoparticles are supported in the walls of hollow nitrogen-doped porous carbon capsules created by the decomposition of the organic components of the precursor. The capsules prevent sintering and detachment of the nanoparticles, and their porosity allows for efficient mass transport. To demonstrate the utility of producing a broad library of supported multicomponent metal nanoparticles, we tested their electrocatalytic performance toward the hydrogen evolution reaction and oxygen evolution reaction. We discovered functional relationships between the composition of the nanoparticles and their electrochemical activity and identified the PtNiCu and PtNiCuFe nanoparticles as particularly efficient catalysts. This highlights how to generate diverse libraries of multicomponent metal nanoparticles that can be synthesized and subsequently screened to identify high-performance materials for target applications.

Facile synthesis of Pd@Ru nanoplates with controlled thickness as efficient catalysts for hydrogen evolution reaction

Pd@Ru nanoplates with controlled thickness were synthesized and exhibited substantially enhanced properties for the hydrogen evolution reaction relative to commercial catalysts.

Probing the Surface of Platinum during the Hydrogen Evolution Reaction in Alkaline Electrolyte

Understanding the surface chemistry of electrocatalysts in operando can bring insight into the reaction mechanism, and ultimately the design of more efficient materials for sustainable energy storage and conversion. Recent progress in synchrotron based X-ray spectroscopies for in operando characterization allows us to probe the solid/liquid interface directly while applying an external potential, applied here to the model system of Pt in alkaline electrolyte for the hydrogen evolution reaction (HER). We employ ambient pressure X-ray photoelectron spectroscopy (AP-XPS) to identify the oxidation and reduction of Pt-oxides and hydroxides on the surface as a function of applied potential, and further assess the potential for hydrogen adsorption and absorption (hydride formation) during and after the HER. This new window into the surface chemistry of Pt in alkaline electrolyte brings insight into the nature of the rate limiting step, the extent of H ad/absorption, and its persistence at more anodic potentials.

Universal dependence of hydrogen oxidation and evolution reaction activity of platinum-group metals on pH and hydrogen binding energy

Understanding how pH affects the activity of hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) is key to developing active, stable, and affordable HOR/HER catalysts for hydroxide exchange membrane fuel cells and electrolyzers. A common linear correlation between hydrogen binding energy (HBE) and pH is observed for four supported platinum-group metal catalysts (Pt/C, Ir/C, Pd/C, and Rh/C) over a broad pH range (0 to 13), suggesting that the pH dependence of HBE is metal-independent. A universal correlation between exchange current density and HBE is also observed on the four metals, indicating that they may share the same elementary steps and rate-determining steps and that the HBE is the dominant descriptor for HOR/HER activities. The onset potential of CO stripping on the four metals decreases with pH, indicating a stronger OH adsorption, which provides evidence against the promoting effect of adsorbed OH on HOR/HER.

Restructuring and Hydrogen Evolution on Pt Nanoparticle

The restructuring of nanoparticles at the in situ condition is a common but complex phenomenon in nanoscience. Here, we present the first systematic survey on the structure dynamics and its catalytic consequence for hydrogen evolution reaction (HER) on Pt nanoparticles, as represented by a magic number Pt44 octahedron (∼1 nm size). Using a first principles calculation based global structure search method, we stepwise follow the significant nanoparticle restructuring under HER conditions as driven by thermodynamics to expose {100} facets, and reveal the consequent large activity enhancement due to the marked increase of the concentration of the active site, being identified to be apex atoms. The enhanced kinetics is thus a "byproduct" of the thermodynamical restructuring. Based on the results, the best Pt catalyst for HER is predicted to be ultrasmall Pt particles without core atoms, a size below ∼20 atoms.

Hydrogen Adsorption on Palladium and Platinum Overlayers: DFT Study

Hydrogen adsorption on twenty different palladium and platinum overlayer surfaces with (111) crystallographic orientation was studied by means of periodic DFT calculations on the GGA-PBE level. Palladium and platinum overlayers here denote either the Pd and Pt mono- and bilayers deposited over (111) crystallographic plane of Pd, Pt, Cu, and Au monocrystals or the (111) crystallographic plane of Pd and Pt monocrystals with inserted one-atom-thick surface underlayer of Pd, Pt, Cu, and Au. The attention was focused on the bond lengths, hydrogen adsorption energetics, mobility of adsorbed hydrogen, and surface reactivity toward hydrogen electrode reactions. Both the ligand and strain effects were considered, found to lead to a significant modification of the electronic structure of Pd and Pt overlayers, described through the position of the d-band center, and tuning of the hydrogen adsorption energy in the range that covers approximately 120 kJmol−1. Mobility of hydrogen adsorbed on studied overlayers was found to be determined by hydrogen-metal binding energy. Obtained results regarding Pd layers on Pt(111) and Au(111) surfaces, in conjunction with some of the recent experimental data, were used to explain its electrocatalytic activity towards hydrogen evolution reaction.