Ozone‐Induced Band Bending on Metal‐Oxide Surfaces Studied under Environmental Conditions

Ozone adsorption and decomposition on metal oxides is of wide interest in technology and in atmospheric chemistry. Here, ozone‐adsorption‐induced band bending is observed on Ti‐ and Fe‐oxide model surfaces under dry and humid conditions. Photoelectron spectroscopic studies indicate the effect of charge transfer to O₃, which limits the surface coverage of the precursor to decomposition reactions. This is also consistent with the negative pressure dependence observed in previous studies. These results contribute to our fundamental understanding of ozone adsorption and decomposition mechanisms on metal oxides of environmental and technological relevance.     

Monte Carlo modeling of ion adsorption at the energetically heterogeneous metal oxide/electrolyte interface: Micro- and macroscopic correlations between adsorption energies

Grand canonical Monte Carlo simulations are carried out for the basic Stern model of the electrical double layer formed at the energetically heterogeneous metal oxide/electrolyte interface. The effect of the global (macroscopic) and local (microscopic) adsorption energies correlations as well as the influence of the model parameter on the surface charge density curves were investigated. The linear dependence of point of zero charge (PZC) as a function of H+ ion adsorption energy proves that the acidic/basic properties of the system are mainly governed by proton uptake/release. Two kinds of systems were taken into account: one neglecting lateral interactions and the other one including them. The effect of electrolyte concentrations as well as the surface heterogeneity on the surface charge density curves were shown too. The presented simulation algorithm allows to model two experimentally observed instances of the metal oxide/electrolyte interface: one possessing a common intersection point (CIP) at pH = PZC and the other one with CIP not equal PZC.     

Kinetic studies on the reaction of methylcobalamin with metal oxides

Aqueous solutions of methylcobalamin (CH₃B₁₂) react with various water-insoluble metal oxides. The decomposition of methylcobalamin follows a kinetic pattern of two parallel first-order reactions. A proposed reaction mechanism involves the attachment of methylcobalamin to the oxide surface, followed by methyl transfer and dissolution of the oxide.     

Modelling the formation and growth of anodic passive films on metals in concentrated acid solutions

Two model approaches to the formation of passive films as adsorbed layers during the active anodic dissolution of a metal in acid and their subsequent growth are presented. The first depicts passivation as proceeding in parallel to active dissolution. Adsorption of water on active surface sites leads to passivation, whereas adsorption of acid leads to active dissolution of the metal. The model is consistent with the impedance response during passivation of Fe and an Fe-20%Mo alloy in concentrated H₃PO₄. The second model is an updated version of the so-called surface charge approach to the mechanism of conduction of anodic passive films. It is based on the assumptions that oxygen vacancies are the main ionic charge carriers and the field strength in the barrier layer is constant. A negative surface charge built up at the film/solution interface via accumulation of metal vacancies accelerates oxygen vacancy transport, thus explaining the pseudoinductive behaviour of the metal/film/electrolyte system under small amplitude a.c. perturbation. The model describes the growth of thin anodic films on Fe, Mo and an Fe-20%Mo alloy in concentrated H₃PO₄. Received: 24 January 1997 / Accepted: 18 April 1997     

Evolution of an iron passive film in a borate buffer solution (pH 8.4)

The evolution under open-circuit conditions of iron passive films formed at 0.8 V_SCE in a borate buffer solution at pH 8.4 was investigated with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The composition of the freshly formed passive film as determined by X-ray photoelectron spectroscopy (XPS) was found to be in agreement with a bilayer model, where the inner layer is composed mainly of iron oxide and the outer layer consists of a hydrated material. Results of XPS measurements also showed that the open-circuit breakdown of passive films was consistent with a reductive dissolution mechanism. When the iron electrode reached an intermediate stage in the open-circuit potential decay (approximately −0.3 V_SCE), the oxide film, containing both Fe(II) and Fe(III), was still protective. The impedance response in this stage exhibited a mixed control by charge transfer at the metal/film and film/solution interfaces and diffusion of point defects through the film. At the final stage of the open-circuit potential decay (approximately −0.7 V_SCE), the oxide film was very thin, and the ratio of Fe³⁺/Fe²⁺ and O²⁻/OH⁻ had decreased significantly. The impedance response also exhibited a mixed charge-transfer–diffusion control, but the diffusion process was related to transport of species in the electrolyte solution resulting from dissolution of the oxide film.     

Electrochemical reactions at a copper electrode in copper-conducting solid electrolytes

Potentiostatic measurements are used to show that, depending on the overvoltage sign, either electrochemical deposition or dissolution of copper occurs at the Cu/Cu₄RbCl₃I₂ interface at overvoltages η > 8–10 mV. At η = 10–100 mV, the reaction rate is limited by the formation and expansion of dissolution centers at the copper surface during anodic polarization and crystallization centers, during cathodic polarization. At η > 120 mV, the reaction rate is limited by charge transfer; the exchange current density is 2.7 mA cm^?2 and the anodic transfer coefficient is ～0.45. Under anodic polarization, formation of electron holes in the electrolyte occurs in parallel with the copper anodic dissolution. Therefore, nonstoichiometry of the electrolyte emerges in the near-electrode layer and divalent copper accumulates there.     

On the relationship between charge distribution, surface hydration, and the structure of the interface of metal hydroxides

The double layer structure of metal (hydr)oxides is discussed. Charge separation may exist between the minimum distance of approach of electrolyte ions and the DDL domain. The corresponding capacitance value of the outer Stern layer is similar to the capacitance value of the inner Stern layer. The extended Stern model implicitly supports a hydration structure at the near-surface with some discrete layering of water and electrolyte ions. The significance of dipole orientation is analyzed theoretically. Dipole theory in combination with a calculated ion charge distribution is compared with the experimental overall charge distribution. Ion charge distribution for various oxyanions has been calculated applying the Brown bond valence concept to the geometry of surface complexes that have been optimized with MO/DFT calculations. The comparison is done in detail for silicic acid adsorption on goethite. In addition, results are discussed for arsenite, carbonate, sulfate, and phosphate, using the same approach. The dipole correction depends on the charge introduced in a neutral surface by ion adsorption, which differs for the various ions studied. The fractional correction factor phi derived for the experimental data agrees with the theoretical value phi(m)=0.17+/-0.02. On an absolute scale, the dipole corrections are usually limited to the range about 0-0.15 v.u. The CD values calculated with MO/DFT are not particularly sensitive (approximately 0.03 v.u.) to the precise Fe-octahedral geometry, which suggests that a calculated CD is a reasonable approximation in ion adsorption modeling for ill-defined Fe-oxides like HFO and natural Fe oxide materials of soils.     

Influence of Zn(II) adsorption on the photocatalytic activity and the production of H2O2 over irradiated TiO2

The photocatalytic activity of semiconductor oxides, in particular TiO₂ powders or colloids, is a complex function of bulk (light absorption and scattering, charge carrier mobility and recombination rate) and surface (structure, defects and reconstruction, charge, presence of adsorbate, surface recombination centers) properties. Among surface modifications, the inner sphere surface complexation of metal cations can change the surface charge of the metal oxide, thus changing the surface activity coefficient of ionic substrates, the band edge positions, as well as the mechanism and kinetic of interfacial electron transfer by blocking surface trapping sites for photogenerated carriers (≡Ti?OH). In this work we show that in anatase/water systems under band-gap irradiation, both the organic substrate (formate) oxidation initiated by photogenerated valence band holes and the formation of hydrogen peroxide from O₂ reduction (by conduction band electrons) is strongly influenced by the presence of Zn²⁺ cations. Depending on the pH, the formate oxidation rate can be enhanced or nearly completely inhibited. The observed result can be rationalized by considering the fraction of ≡Ti?OH surface sites blocked by inner sphere complexation of Zn²⁺ as a function of pH. When this fraction is low, the more positive surface charge favors formate oxidation, whereas when the fraction is high the almost complete blockage of ≡Ti?OH surface sites by Zn²⁺ stops almost entirely formate oxidation. Interestingly, the surface complexation of Zn²⁺ is accompanied by an increasing production of H₂O₂ during formate degradation in the presence of O₂. Zn(II) cations are not complexed by peroxide/superoxide species derived from O₂ reduction. When ≡Ti?OH sites are blocked by Zn²⁺, the complexation on the TiO₂ surface of peroxide/superoxide species is inhibited, hindering their further transformation. The results presented demonstrate that the combined effect of pH and surface complexation of redox inert cations greatly influences both the oxidative and reductive processes during the photocatalytic process over TiO₂.     

Reactivity of metal oxides: Thermal and photochemical dissolution of MO and MFe2O4 (M=Ni, Co, Zn)

Dissolution rates of NiO, CoO, ZnO, α-Fe₂O₃ and the corresponding ferrites in 0.1 mol dm⁻³ oxalic acid at pH 3.5 were measured at 70 °C. The dissolution of simple oxides proceeds through the formation of surface metal oxalate complexes, followed by the transfer of surface complexes (rate-determining step). At constant pH, oxalate concentration and temperature, the trend in the first-order rate constant for the transfer of the surface complexes (k_Me; Me=Ni, Co, Zn, Fe) parallels that of water exchange in the dissolved metal ions (k_−w). Thus, the most important factor determining the rates of dissolution of metal oxides is the lability of Me-O bonds, which is in turn defined by the electronic structure of the metal ion and its charge/radius ratio. UV (384 nm) irradiation does not increase significantly the dissolution rates of NiO, CoO and ZnO, whereas hematite is highly sensitive to UV light. For ferrites, the reactivity order is ZnFe₂O₄>CoFe₂O₄?NiFe₂O₄. Dissolution is congruent, with rates intermediate between those of the constituent oxides, Fe₂O₃ and MO (M=Co, Ni, Zn), reflecting the behavior of very thin leached layers with little Zn and Co, but appreciable amounts of Ni. The more robust Ni²⁺ labilizes less the corresponding ferrite. The correlation between log k_M and log k_−w is somewhat blurred and displaced to lower k_M values. Fe(II), either photogenerated or added as salt, enhances the rate of Fe(III) phase transfer. A simple reaction mechanism is used to interpret the data.     

Controlled Assembly of Cu/Co-Oxide Beaded Nanoclusters on Thiolated Graphene Oxide Nanosheets for High-Performance Oxygen Evolution Catalysts

The use of water splitting modules is highly desired for the sustainable production of H₂ as a future energy carrier. However, the sluggish kinetics and demand of high anodic potential are the bottlenecks for half-the cell oxygen evolution reaction (OER), which severely hamper the overall conversion efficiency. Although transition metal oxides based electrocatalysts have been envisioned as cost-effective and potential contenders for this quest, nevertheless, their low conductivity, instability, and limited number of active sites are among the common impediments that need to be addressed to eventually enhance their inherent catalytic potential for enhanced OER activity. Herein, the controlled assembly of transition metal oxides, that is, Cu@CuO_x nanoclusters (NCs, ≈2 nm) and Co@CoO_x beaded nanoclusters (BNCs, ≈2 nm), on thiol-functionalized graphene oxide (G-SH) nanosheets is reported to form novel and highly efficient electrocatalysts for OER. The thiol (-SH) functionality was incorporated by selective epoxidation on the surface of graphene oxide (GO) to achieve chemically exfoliated nanosheets to enhance its conductivity and trapping ability for metal oxides in nanoscale dimensions (≈2 nm). During the electrocatalytic reaction, overpotentials of 290 mV and 310 mV are required to achieve a current density of 10 mA cm⁻² for BNCs and NCs, respectively, and the catalysts exhibit tremendous long-term stability (≈50 h) in purified alkaline medium (1 m KOH) with no dissolution in the electrolyte. Moreover, the smaller Tafel slopes (54 mV/dec for BNCs and 66 mV/dec for NCs), and a Faradic efficiency of approximately 96 % indicate not only the selectivity but also the tailored heterogeneous electrons transfer (HET) rate, which is required for fast electrode kinetics. It is anticipated that such ultrasmall metal oxide nanoclusters and their controlled assembly on a conducting surface (G-SH) may offer high electrochemical accessibility and a plethora of active sites owing to the drastic decrease in dimensions and thus can synergistically ameliorate the challenging OER process.     

Charge state of metal atoms on oxide supports: a systematic study based on simulated infrared spectroscopy and density functional theory

A long standing question in the study of supported clusters of metal atoms in the properties of metal–oxide interfaces is the extent of metal–oxide charge transfer. However, the determination of this charge transfer is far from straight forward and a combination of different methods (both experimental and theoretical) is required. In this paper, we systematically study the charging of some adsorbed transition metal atoms on two widely used metal oxides surfaces [α-Al₂O₃ (0001) and rutile TiO₂ (110)]. Two procedures are combined to this end: the computed vibrational shift of the CO molecule, that is used as a probe, and the calculation of the atoms charges from a Bader analysis of the electron density of the systems under study. At difference from previous studies that directly compared the vibrational vawenumber of adsorbed CO with that of the gas phase molecule, we have validated the procedure by comparison of the computed CO stretching wavenumbers in isolated monocarbonyls (MCO) and their singly charged ions with experimental data for these species in rare gas matrices. It is found that the computational results correctly reproduce the experimental trend for the observed shift on the CO stretching mode but that care must be taken for negatively charged complexes as in this case there is a significative difference between the total charge of the MCO complex and the charge of the M atom. For the supported adatoms, our results show that while Cu and Ag atoms show a partial charge transfer to the Al₂O₃ surface, this is not the case for Au adatoms, that are basically neutral on the most stable adsorption site. Pd and Pt adatoms also show a significative amount of charge transfer to this surface. On the TiO₂ surface our results allow an interpretation of previous contradictory data by showing that the adsorption of the probe molecule may repolarize the Au adatoms, that are basically neutral when isolated, and show the presence of highly charged Au^δ+–CO complexes. The other two coinage metal atoms are found to significatively reduce the TiO₂ surface. The combined use of the shift on the vibrational frequency of the CO molecule and the computation of the Bader charges shows to be an useful tool for the study the charge state of adsorbed transition metal atoms and allow to rationalize the information coming from complementary tools.     

Bi-affinity Electrolyte Optimizing High-Voltage Lithium-Rich Manganese Oxide Battery via Interface Modulation Strategy

The practical implementation of high-voltage lithium-rich manganese oxide (LRMO) cathode is limited by the unanticipated electrolyte decomposition and dissolution of transition metal ions. The present study proposes a bi-affinity electrolyte formulation, wherein the sulfonyl group of ethyl vinyl sulfone (EVS) imparts a highly adsorptive nature to LRMO, while fluoroethylene carbonate (FEC) exhibits a reductive nature towards Li metal. This interface modulation strategy involves the synergistic use of EVS and FEC as additives to form robust interphase layers on the electrode. As-formed S-endorsed but LiF-assisted configuration cathode electrolyte interphase with a more dominant −SO₂− component may promote the interface transport kinetics and prevent the dissolution of transition metal ions. Furthermore, the incorporation of S component into the solid electrolyte interphase and the reduction of its poorly conducting component can effectively inhibit the growth of lithium dendrites. Therefore, a 4.8 V LRMO/Li cell with optimized electrolyte may demonstrate a remarkable retention capacity of 97 % even after undergoing 300 cycles at 1 C.     

Dissolution of pure and substituted goethites controlled by the surface reaction under conditions of abrasive stripping voltammetry

Pure goethites and Al-, Cr-, and Mn-goethites, as synthetic and natural products, were used to establish the conditions for electrochemical reductive dissolution following surface reaction kinetics. In diluted perchloric acid and at reaction rate coefficients of the order of 10⁻⁴s⁻¹, the γ parameters in the kinetic equation J/N ₀ = k(N/N ₀)^γ (where J is the reaction rate and N and N ₀ are actual and total molar amounts of a solid reactant) were in the range expected for the shape-preserving dissolution of the particles with a certain size and reactivity distribution function. The same range of γ was found using the dissolution of goethites by a chemical reaction via oxalate-ferrous ion surface complexation. The importance of the charge transfer coefficient to describe the iron oxide reactivitie s was highlighted as it is sensitive to the synthetic route and also to the substitution of iron. Received: 20 December 1996 / Accepted: 24 February 1997     

Effect of Electrolyte Concentration on the Stern Layer Thickness at a Charged Interface

The chemistry and physics of charged interfaces is regulated by the structure of the electrical double layer (EDL). Herein we quantify the average thickness of the Stern layer at the silica (SiO₂) nanoparticle/aqueous electrolyte interface as a function of NaCl concentration following direct measurement of the nanoparticles’ surface potential by X‐ray photoelectron spectroscopy (XPS). We find the Stern layer compresses (becomes thinner) as the electrolyte concentration is increased. This finding provides a simple and intuitive picture of the EDL that explains the concurrent increase in surface charge density, but decrease in surface and zeta potentials, as the electrolyte concentration is increased.     

Specimen transfer from the electrolyte to the UHV in a closed system and some examinations of the double layer on Cu

A transfer system is described which permits the electrochemical preparation of specimens in a purified argon atmosphere and their transport into the UHV for surface analysis. This transfer prevents contamination and oxide formation on semi-noble metals. Reactive metals from only a few monolayers of oxide. This permits examination of electrochemically prepared metal surfaces, which is otherwise not possible. For hydrophobic copper surfaces, the composition of the electrical double layer may be studied. The extraction of the electrode strips the electrolyte off in the vicinity of the Helmholtz layer. For NaClO₄ solutions, the amount of Na⁺ ions and the excess charge decrease linearly with the electrode potential in agreement with a constant electrode capacity. The formation of a prepassive and passive layer leads to a pronounced increase of adsorbed Na⁺ ions. For Cs₂SO₄, specific and co-adsorption of both ions is observed with a minimum in the region of the potential of zero charge.     

Reactivity at the mineral-water interface: dissolution and inhibition

The reactivity of the mineral-water interface is often interpreted with the help of models used in electrochemistry, in solution coordination chemistry and in crystallography. Progress in understanding mechanisms of growth and dissolution of crystals and the inhibition of these processes depends on a better integration of these models. It is shown that dissolution can be explained in terms of a ligand exchange process; simplified rate laws for proton- and ligand-protonated dissolution rates, being related to surface bound protons and ligands, respectively, can be derived. Further refinement in interpreting surface reactivity comes from an appreciation of the molecular structures at the mineral water interface; here significant advances have been made by X-ray absorption spectroscopy, especially EXAFS (Extended X-ray Absorption Fine Structure spectroscopy), which permit distinction to be made between outer-sphere and inner-sphere surface complexes, and in many cases to determine the structure of the surface species at different crystallographic planes (e.g., bi-nuclear or mono-nuclear linkage of ligands on metal ions to surface metal centers). Such information coupled with solution-chemical studies on the extent of adsorption can provide new insight into the mechanisms of dissolution reactions and their inhibition and surface poisoning. A few experimental results are given to exemplify the factors that enhance and inhibit the non-reductive (EDTA) and reductive dissolution (by H₂S) of Fe(III)(hydr)oxides. Binuclear surface complexes by multivalent cations and by oxoanions, such as phosphate, arsenate and borate, are believed to be efficient inhibitors for oxide dissolution because they form bi- or multinuclear innersphere surface complexes that can bridge two or more metal centers in the surface lattice; the simultaneous removal of such bi- or multinuclear surface complexes from the surface is energetically unfavorable. Proton and ligand promoted dissolution reactions and their inhibition by oxoanions and bi- or multinuclear surface complexes are not only relevant in geochemistry (weathering, soil-formation, transfer of elements and pollutants) but also in metallic corrosion, formation and breakdown of passive oxide films.     

Determination of pH value of isoelectric solution and identification of passive iron surface phases using immersion method

Using the method of phase modeling, the pH values of solutions corresponding to the uncharged surface of passive iron and ferric oxide γ-Fe₂O₃ (pH₀) are compared. According to the theory of connected places, the charge of metal oxide surface is determined by the adsorption or desorption of hydrogen ions leading to a change in the potential drop at the oxide/solution interface. Preliminarily passivated iron electrode was washed with twice-distilled water and placed into 0.5 M NaNO₃ solution with various pH values; the variation in the potential (ΔE) with time was studied. The pH₀ value for passive electrode under the open-circuit conditions was determined by the dependence of ΔE on the pH value (pH₀ 6.2 ± 0.1). The pH₀ value was close to that for γ-Fe₂O₃ (pH₀ 6.2), which was determined by the method of potentiometrical titration of oxide suspension in the nitrate solution. The introduction of surface-active ions Ba²⁺ and Cl^? changes the charge of passive iron surface: Ba²⁺ ions increase the electrode potential, while Cl^? ions decrease it. Comparing the pH₀ values for passive electrode and metal oxides, one can identify the composition of passive electrode surface.     

Promotion effect of metal oxides on C-O bond dissociation in CO hydrogenation over Rh/SiO2 Catalyst — possible role of partially reduced state cations

In CO hydrogenation over Rh/SiO₂ catalysts, the effect of additive metal oxides on C-O bond dissociation was studied by using pulse surface reaction rate analysis (PSRA). The addition of oxides of Al, Ti, Cr, V, and Mn resulted in an increase in the rate constant for the dissociation according to this sequence, while the oxides of Cu, Zn, and Ag added decreased the rate constant to almost the same extent. In contrast to these metal oxides, MoO₃ and WO₃ did not change the dissociation activity. CO adsorption measurement indicated that all of the added metal oxides covered a considerable portion of the Rh metal surface, although the efficiency of covering was different from one metal oxide to another. Covering the Rh metal surface with an added metal oxide should decrease the rate constant of C-O bond dissociation, because ensemble sites, consisting of a group of surface Rh atoms and considered necessary for the dissociation, were destroyed. The suppression effect resulted from the destruction of the ensemble sites by adding the oxides of Cu, Zn, and Ag. For other metal oxides, temperature-programmed reduction (TPR) or O₂ uptake measurement revealed that the added oxides, especially those existing on the Rh metal surface, were in a partially reduced state under reaction conditions. Owing to its high affinity for an oxygen atom, the cation in a partially reduced state participated in the reaction in such a way that the oxygen end of adsorbed CO species was bound to the cation so as to dissociate the C-O bond, which resulted in promotion of the dissociation. The observed promotion was explained in terms of the enhancement owing to the high affinity sufficient to overcome the suppression caused by destroying ensemble sites. Lack of the promotion effect of MoO₃ and WO₃ might result from a balance between promotion due to the high affinity of the partially reduced Mo or W and suppression caused by destroying ensemble sites. Excellent correlation was observed between the intrinsic activity increase, from which the suppression effect was excluded, and the heat of formation of metal oxide including MoO₃ and WO₃. Since the heat of formation of metal oxide is considered to be a measure of the affinity, this correlation supports the idea that the high affinity of additive cations for an oxygen atom is of primary importance in the promotion of C-O bond dissociation in CO hydrogenation.     

Characteristics of Pt Electrode Activated by Tb1 − xCexO2 − α Films in Contact with ZrO2 + 10 mol % Y2O3 Electrolyte

Porous platinum electrodes on ZrO₂ + 10 mol % Y₂O₃ solid electrolyte (YSZ) are activated by Tb_{1 ? x}Ce_xO_{2 ? α} (x = 0; 0.15; 0.33; 0.5; 1.0) mixed oxides by impregnation, and their polarization characteristics are studied. The activation is carried out under the conditions that an oxide activator nanofilm forms on the electrolyte surface as a result of heat treatment of the electrode. The activation is performed by impregnating the electrodes with low-concentrated alcohol solution of terbium and cerium nitrates (1.5% as recalculated to the oxides) and subsequent slow heating (≤50°C/h) to 850°C. An average thickness of the film on the electrolyte after a single activation (≈0.1 mg oxides/cm²) is estimated at 10–20 nm. The electrodes of Pt|YSZ|Pt cell activated by Tb_{1 ? x}Ce_xO_{2 ? α} films are studied by the impedance method in the oxidative and reductive atmospheres in the range of 700 to 500°C. The polarization conductivities of the activated electrodes increase by 2–3 orders of magnitude. The studied electrodes are discussed within the model of compact oxide electrodes, where platinum plays the role of collector. The advantage of these electrodes is that they can work both in the oxidative and reductive conditions. According to the aggregate of the properties, Tb_{1 ? x}Ce_xO_{2 ? α} compounds at x = 0.3–0.5 are recommended for activation.

     

Negative Charging of Transition‐Metal Phosphides via Strong Electronic Coupling for Destabilization of Alkaline Water

Heterogeneous electrocatalysis typically involves charge transfer between surface active sites and adsorbed species. Therefore, modulating the surface charge state of an electrocatalyst can be used to enhance performance. A series of negatively charged transition‐metal (Fe, Co, Ni, Cu,and NiCo) phosphides were fabricated by designing strong electronic coupling with hydr(oxy)oxides formed in situ. Physicochemical characterizations, together with DFT computations, demonstrate that strong electronic coupling renders transition‐metal phosphides negatively charged. This facilitates destabilization of alkaline water adsorption and dissociation to result in significantly improved H₂ evolution. Negatively charged Ni₂P/nickel hydr(oxy)oxide for example exhibits a significantly low overpotential of 138 mV at 100 mA cm^?2, superior to that without strong electronic coupling and also commercial Pt/C.