Proton Adsorption Research Articles

Spectroelectrochemical determination of the conduction band level of mesoporous titanium dioxide semiconductor in diverse reaction media

AbstractThe conduction band edge (ECB) energy levels of a mesoporous TiO2 film were investigated in aprotic dimethylformamide (DMF) and aqueous media to explore the influence of various proton additives and electron donors. Spectroelectrolysis (SE) technique was employed to measure the ECB in non‐aqueous solvents, revealing a significantly negative ECB in dry non‐aqueous solvents compared to values obtained in aqueous solvents. In non‐aqueous DMF, the ECB of TiO2 was found to be highly dependent on the proton‐donating additive due to the establishment of a proton adsorption–desorption equilibrium, reaching –(1.42–1.94) V versus SCE. The introduction of a well‐known electron donor, 1,3‐dimethyl‐2‐phenyl‐1,3‐dihydrobenzimidazole (BIH) led to a slight positive shift in the TiO2 ECB, indicating that the electron donor contributes to the to the CB energetics of the mesoporous TiO2 films. Under aqueous conditions and in the presence of various electron donors (TEA, TEOA, ascorbic acid, EDTA•2Na, and sodium ascorbate), the proton‐donating/accepting capacity of the additive significantly influenced the pH of the aqueous solvent, causing changes in the TiO2 ECB across the electrolyte solution. This study emphasizes the crucial role of proton additives and electron donors in influencing the CB energetics of mesoporous TiO2 electrodes and aims to determine the extent to which the ECB of TiO2 can shift as a result of the adsorption and intercalation of protons on its surface. The findings obtained herein contribute to the understanding of the energy efficiency of TiO2‐mediated photocatalytic systems in various solvent environments.

Intensifying the Supported Ruthenium Metallic Bond to Boost the Interfacial Hydrogen Spillover Toward pH‐Universal Hydrogen Evolution Catalysis

AbstractThe effectuation of pH‐universal electrocatalysis is highly attractive but still challenging for the hydrogen evolution reaction (HER). It appeals for not only the facilitated electron transport but also the kinetical proton mass transfer. In this study, a via‐hole Ru/MoO2 confined heterostructure is profiled as a metal‐support platform for the electron/mass transfer‐boosted pH‐universal HER studies. It is indicated that the as‐formed Ru─O─Mo bridge can modulate the electronic transport at the interface, and the proton adsorption and transfer are kinetically derived by the intensified metallic Ru─Ru bond. Resultantly, the Ru/MoO2 heterostructure stably attains the Pt‐beyond HER activity with an ultralow overpotential of 9.2 mV at 10 mA cm−2 in 1 m KOH, and also achieves the competitive HER activity and stability in the acidic/neutral electrolytes. Both the experimental and computational results reveal the accelerated HER kinetics is attributable to the intensive mass transfer through the interfacial Ru→MoO2 hydrogen spillover effect. This work opens up the opportunities to rationalize the advanced metal‐support HER electrocatalysts through the interfacial hydrogen spillover effect and metallic bond engineering.

Water‐Tolerant Superbase Polyoxometalate [H2(Nb6O19)]6− for Homogeneous Catalysis

AbstractHere, doubly protonated Lindqvist‐type niobium oxide cluster [H2(Nb6O19)]6–, fabricated by microwave‐assisted hydrothermal synthesis, exhibited superbase catalysis for Knoevenagel and crossed aldol condensation reactions accompanied by activating C−H bond with pKa >26 and proton abstraction from a base indicator with pKa=26.5. Surprisingly, [H2(Nb6O19)]6− exhibited water‐tolerant superbase properties for Knoevenagel and crossed aldol condensation reactions in the presence of water, although it is well known that the strong basicity of metal oxides and organic superbase is typically lost by the adsorption of water. Density functional theory calculation revealed that the basic surface oxygens that share the corner of NbO6 units in [H2(Nb6O19)]8− maintained the negative charges even after proton adsorption. This proton capacity and the presence of un‐protonated basic sites led to the water tolerance of the superbase catalysis.

Water-Tolerant Superbase Polyoxometalate [H2(Nb6O19)]6- for Homogeneous Catalysis.

Here, doubly protonated Lindqvist-type niobium oxide cluster [H2(Nb6O19)]6-, fabricated by microwave-assisted hydrothermal synthesis, exhibited superbase catalysis for Knoevenagel and crossed aldol condensation reactions accompanied by activating C-H bond with pKa >26 and proton abstraction from a base indicator with pKa=26.5. Surprisingly, [H2(Nb6O19)]6- exhibited water-tolerant superbase properties for Knoevenagel and crossed aldol condensation reactions in the presence of water, although it is well known that the strong basicity of metal oxides and organic superbase is typically lost by the adsorption of water. Density functional theory calculation revealed that the basic surface oxygens that share the corner of NbO6 units in [H2(Nb6O19)]8- maintained the negative charges even after proton adsorption. This proton capacity and the presence of un-protonated basic sites led to the water tolerance of the superbase catalysis.

Halide-modulated Hollow-Fiber Cu penetration electrode boosts Ampere-Level CO2 electroreduction to multicarbon products

Electroreduction of CO2 to chemical fuels is desirable for the economically viable use of CO2 and consumption of renewable electricity. Efficient production of C2+ on Cu-based catalysts remains a challenge. Herein, a copper hollow fiber penetration electrode with a striking C–C coupling capability by virtue of modulating the electronic states through halide ion coordinated adsorption. An efficient C2+ production with a FE of 68.8 % at 2.1 A cm−2 in 3.0 M KI and remained stable during 120-h electrolysis at 2.0 A cm−2, outperforming reported catalytic performance, which is the result of combined effect of penetration effect and halide ion coordinated adsorption, which promotes the transfer of electrons to CO2, reduces the C–C coupling energy and suppresses proton adsorption, thereby reducing hydrogen evolution.

Micro-mechanism investigation of hydrogen evolution reaction on anti-perovskite Ni3InN considering doping and strain effects

Anti-perovskites are considered as promising high-efficiency catalysts for hydrogen evolution reaction (HER) due to their low cost, adjustable composition, and small water dissociation kinetic barriers. Accounting strain effects, transition metal doping effects and solvent effects, we calculate HER micro-mechanism on anti-perovskite Ni3InN and conclude that HER on Ni3InN can be divided into two steps, rapid proton adsorption at the Bridge site and favorable H2 desorption at the Hollow site. We obtained 2 doping elements (Pt and Ir) from 20 transition metal elements that can enhance HER catalytic performance of Ni3InN. It is worth noting that applying a certain strain is beneficial for the catalytic performance of some doped Ni3InN (e.g. +2 %, +1% for Pt), while harmful for others (e.g. Ir). Our work provides a new perspective for the application of anti-perovskites in HER, which is meaningful for the development of HER catalysts.

Green and alcohol-free H2O2 generation paired with simultaneous contaminant treatment enabled by sulfur/cyano-modified g-C3N4 with efficient oxygen activation and proton adsorption

A S atom and cyano group co-modified carbon nitride was synthesized for alcohol-free H2O2 generation paired with simultaneous contaminant treatment. S atoms facilitate oxygen adsorption and cyano groups lead to the promotion of H+ adsorption.

Amino-functionalization enhanced CO2 reduction reaction in pure water.

The electrochemical reduction of carbon dioxide (CO2RR) to carbon monoxide represents a cost-effective pathway towards realizing carbon neutrality. To suppress the hydrogen evolution reaction (HER), the presence of alkali cations is critical, which can however lead to precipitate formation on the electrode, adversely impacting the device stability. Employing pure water as the electrolyte in zero-gap CO2 electrolyzers can address this challenge, albeit at the cost of diminished catalyst performance due to the absence of alkali cations. In this study, we introduce a novel approach by implementing amino modifications on the catalyst surface to mimic the function of alkali metal cations, while simultaneously working in pure water. This modification enhances the adsorption of carbon dioxide and protons, thereby facilitating the CO2RR while concurrently suppressing the HER. Utilizing this strategy in a zero-gap CO2 electrolyzer with pure water as the anolyte resulted in an impressive carbon monoxide faradaic efficiency (FECO) of 95.5% at a current density of 250 mA cm-2, while maintaining stability for over 180 hours without any maintenance.

Enhanced Electrocatalytic Nitrate Reduction to Ammonia Using Functionalized Multi-Walled Carbon Nanotube-Supported Cobalt Catalyst.

Ammonia (NH3) is vital in modern agriculture and industry as a potential energy carrier. The electrocatalytic reduction of nitrate (NO3-) to ammonia under ambient conditions offers a sustainable alternative to the energy-intensive Haber-Bosch process. However, achieving high selectivity in this conversion poses significant challenges due to the multi-step electron and proton transfer processes and the low proton adsorption capacity of transition metal electrocatalysts. Herein, we introduce a novel approach by employing functionalized multi-walled carbon nanotubes (MWCNTs) as carriers for active cobalt catalysts. The exceptional conductivity of MWCNTs significantly reduces charge transfer resistance. Their unique hollow structure increases the electrochemical active surface area of the electrocatalyst. Additionally, the one-dimensional hollow tube structure and graphite-like layers within MWCNTs enhance adsorption properties, thus mitigating the diffusion of intermediate and stabilizing active cobalt species during nitrate reduction reaction (NitRR). Using the MWCNT-supported cobalt catalyst, we achieved a notable NH3 yield rate of 4.03 mg h-1 cm-2 and a high Faradaic efficiency of 84.72% in 0.1 M KOH with 0.1 M NO3-. This study demonstrates the potential of MWCNTs as advanced carriers in constructing electrocatalysts for efficient nitrate reduction.

N-Doped Norbornane sp2 Carbon Framework: An Efficient Electrocatalyst for Oxygen Reduction and Hydrogen Evolution Reaction

At present, development of Pt free bifunctional electrocatalyst for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is necessary for the advancement of sustainable and cost-effective solutions for energy conversion and storage technology. In this direction, herein we report N doped sp2 hybridized carbon framework (N-CF) as a metal-free electrocatalyst for ORR and HER. This work inspects the effect of N doping that converts a hybrid structure of CF {Norbornane or bicyclo [2, 2, 1] heptane structure} into planar N-CF. A series of N-doped CF with different doping concentrations has been prepared using a facile and cost-effective technique. This robust electrocatalysts exhibits a promotional effect in the activity, porosity, thermal and electrochemical stability for the ORR and HER reactions. A rich delocalized electronic density of the sp2 bounded N species helps in modulating antibonding state of molecular oxygen and facilitates the breakage of O=O bond in ORR. It also promotes proton adsorption via bonding between proton and valence electron rich catalyst surface to aid HER. The research sought to investigate the employability of N-CF for fabricating sustainable energy devices with electrocatalyst possessing multiple electrocatalytic activities for ORR and HER. Figure 1

Electrochemical N2-to-NH3 with high faradaic efficiency on ZrO2/carbon quantum dots catalysts in neutral electrolyte

Electrochemical nitrogen reduction (NRR) to synthesize NH3 is limited by low Faraday efficiency (FE). Developing electrocatalysts that can efficiently adsorb/activate N2 and suppress hydrogen evolution reaction (HER) to enhance FE is needed. In this work, x-ZrO2/CQDs-T series catalysts were successfully prepared. The results demonstrate that: (I) The appropriate introduction of carbon quantum dots (CQDs) effectively enhances the surface adsorption capacity of ZrO2/CQDs for N2. (II) By high-temperature calcination eliminates the alkaline functional group (-NH2) of CQDs, which reduces the basicity of ZrO2/CQDs catalyst and inhibits the adsorption of protons on the catalyst surface. (III) Due to the semiconductor properties of ZrO2, the charge transfer efficiency of ZrO2/CQDs catalyst is significantly reduced, thereby weakening the binding of electrons to the adsorbed protons. As a result, 1-ZrO2/CQDs-750 catalyst appropriately and effectually restricts the accessibility of protons/electrons and promotes more N2 molecules to occupy active sites, thus achieving up to 66.62 % FE, which is superior to most reported NRR catalysts so far. Meanwhile, electrochemical in situ ATR-SEIRAS technique reveals that 1-ZrO2/CQDs-750 catalyst surface occurs in associative alternating reactions. The introduction of CQDs not only effectively affects the adsorption of N2 and N-related intermediates on ZrO2/CQDs catalyst and limits the proton/electron accessibility to improve FE of NRR, but also promotes the exposure of active sites to increase NH3 yield.

Multisite Cocatalysis: Single atomic Pt2+/Pt0 active sites synergistically improve the simulated sunlight driven H2O-to-H2 conversion performance of Sb2S3 nanorods

Single atomic metal (SAM) cocatalysis is a potential strategy to improve the performance of photocatalytic materials. However, the cocatalytic mechanism of SAM sites in different valence states is rarely reported. Herein, single atomic Pt2+/Pt0 active sites were anchored on Sb2S3 nanorods to synergistically improve the photoactivity for hydrogen production under simulated sunlight. Experimental results and density functional theory calculations indicated that the coexistence of single atomic Pt2+/Pt0 sites synergistically improves the broadband light harvesting and promotes the Sb2S3-to-Pt electron transfer following inhibited photoexciton recombination kinetics and enhanced H proton adsorption capacity, resulting higher and more durable photoactivity for hydrogen production. Therefore, the optimal Sb2S3-Pt0.9‰ composite catalyst achieved remarkably enhanced hydrogen evolution rate of 1.37 mmol∙g−1∙h−1 (about 105-fold greater of that of Sb2S3 NRs) under faintly alkaline condition, and about 5.41 % of apparent quantum yield (AQY700 nm) was achieved, which shows obvious superiority in hydrogen production by contrasting with the reported Sb2S3-based photocatalysts and conventional semiconductor photocatalytic materials modified with noble metals. This study elucidate a well-defined mechanism of multisite cocatalysis for photoactivity improvement.

Polymer Modification Strategy to Modulate Reaction Microenvironment for Enhanced CO2 Electroreduction to Ethylene

AbstractModulation of the microenvironment on the electrode surface is one of the effective means to improve the efficiency of electrocatalytic carbon dioxide reduction (eCO2RR). To achieve high conversion rates, the phase boundary at the electrode surface should be finely controlled to overcome the limitation of CO2 solubility in the aqueous electrolyte. Herein, we developed a simple and efficient method to structure electrocatalyst with a superhydrophobic surface microenvironment by one‐step co‐electrodeposition of Cu and polytetrafluoroethylene (PTFE) on carbon paper. The super‐hydrophobic Cu‐based electrode displayed a high ethylene (C2H4) selectivity with a Faraday efficiency (FE) of 67.3 % at −1.25 V vs. reversible hydrogen electrode (RHE) in an H‐type cell, which is 2.5 times higher than a regular Cu electrode without PTFE. By using PTFE as a surface modifier, the activity of eCO2RR is enhanced and water (proton) adsorption is inhibited. This strategy has the potential to be applied to other gas‐conversion electrocatalysts.

Polymer Modification Strategy to Modulate Reaction Microenvironment for Enhanced CO2 Electroreduction to Ethylene.

Modulation of the microenvironment on the electrode surface is one of the effective means to improve the efficiency of electrocatalytic carbon dioxide reduction (eCO2 RR). To achieve high conversion rates, the phase boundary at the electrode surface should be finely controlled to overcome the limitation of CO2 solubility in the aqueous electrolyte. Herein, we developed a simple and efficient method to structure electrocatalyst with a superhydrophobic surface microenvironment by one-step co-electrodeposition of Cu and polytetrafluoroethylene (PTFE) on carbon paper. The super-hydrophobic Cu-based electrode displayed a high ethylene (C2 H4 ) selectivity with a Faraday efficiency (FE) of 67.3 % at -1.25 V vs. reversible hydrogen electrode (RHE) in an H-type cell, which is 2.5 times higher than a regular Cu electrode without PTFE. By using PTFE as a surface modifier, the activity of eCO2 RR is enhanced and water (proton) adsorption is inhibited. This strategy has the potential to be applied to other gas-conversion electrocatalysts.

Pyrite copper nickel sulfide for stable hydrogen evolution reaction in alkaline media

The alkaline hydrogen evolution reaction is a promising solution to meet future energy demand due to the sustainable production of hydrogen via water electrolysis. The development of copper nickel sulfide (CuNiS) electrocatalysts for hydrogen evolution reaction (HER) relies on robust active sites without degradation. However, the performance of CuNiS depends on the nature of sulfur precursors and complexing agents since the copper and sulfur oxidation states determine the adsorption and release of H2. The CuNiS synthesized with thioacetamide and 3-mercaptopropionic acid as sulfur source and complexing agent, respectively, at 100°C for 10h delivered a lower overpotential of −96 mV to achieve a current density of −10 mA cm−2 in 1 M KOH electrolyte. The positive and negative shifts in binding energy peaks of Ni and S, respectively, caused charge redistribution and charge transfer between metals and S. The transfer of electrons from Ni to Cu atoms decreases the hydrogen binding energy and accelerates the Had desorption process, which leads to the subsequent formation of H2. Moreover, the negative shift in S improves the electron occupation, which helps with proton adsorption and the release of H2.

Differences in the Physicochemical Properties of Wildfire Generated Pyrogenic Carbon and Biochar

Pyrogenic carbon (PyC) results from the pyrolysis of organic materials through thermal decomposition at high temperatures in low oxygen environments (I.B.I. 2012). The broad term includes many forms of thermochemically altered carbon, including charcoal, black carbon, soot, and biochar (Scott et al. 2014), and consists of a pyrolyzed carbon fraction as well as an inorganic ash or mineral fraction. PyC is produced naturally during forest fires, where it forms at potentially high temperatures (up to 1200 °C) for very short periods of time (seconds to minutes for temperatures >300 °C; Santin et al. 2016a). Wildfire derived PyC has been shown to be a significant component of the carbon cycle, with an estimated 32 Tg of PyC cycled through aquatic environments annually (Santin et al. 2016b). Man-made biochar is generated under controlled conditions via pyrolysis in furnaces at controlled temperatures and under anoxic conditions (Ahmad et al. 2014), typically up to 700 °C, for longer periods of time (up to ~6 hours). Several studies have investigated the surface chemistry of biochar and its ability to remove metals from aqueous solution (e.g., Alam et al. (2018a), Alam et al. (2018b)). However, PyC produced during natural pyrogenic activity such as wild fires, is produced under highly variable temperatures and atmospheric conditions, in the presence of numerous and variable microenvironments which are challenging to measure (Scott et al. 2014), and its surface chemistry and reactivity is not well understood. To fill this gap, we investigate the physicochemical properties including the proton and metal adsorption potential of wildfire generated PyC (WF-PyC) collected from 4 locations within a recent forest fire along the Western slope of Mount Hunter, near Golden, British Columbia. We explored the binding capacity of a model cation (species of Cd2+) under a range of environmentally relavent pH conditions (3-9) and then compared the findings to the adsorption potential of synthetically generated biochar produced from the same biomass. Fourier transform infrared (FTIR) and Raman spectroscopy was used to constrain the number and types of surface functional groups, and the coordination environment of Cd2+ ions bound to WF-PyC and biochar. Potentiometric titrations were performed and modelled to calculate the acidity constants associated with each site and the total reactive surface area of both biochar and WF-PyC. Our results demonstrate greater reactivity to Cd2+ associated with WF-PyC, not replicated in synthetic biochar of an equivalent biomass (Fig. 1). This both provides insight to the potential of WF-PyC to play a critical role as a vector for elemental transport in natural systems and also makes apparent the need to understand the pyrolysis conditions during forest fires to improve our understanding of its role in global metals transport and cycling.

Pd Loaded NiCo Hydroxides for Biomass Electrooxidation: Understanding the Synergistic Effect of Proton Deintercalation and Adsorption Kinetics.

The key issue in the 5-hydroxymethylfurfural oxidation reaction (HMFOR) is to understand the synergistic mechanism involving the protons deintercalation of catalyst and the adsorption of the substrate. In this study, a Pd/NiCo catalyst was fabricated by modifying Pd clusters onto a Co-doped Ni(OH)2 support, in which the introduction of Co induced lattice distortion and optimized the energy band structure of Ni sites, while the Pd clusters with an average size of 1.96 nm exhibited electronic interactions with NiCo support, resulting in electron transfer from Pd to Ni sites. The resulting Pd/NiCo exhibited low onset potential of 1.32 V and achieved a current density of 50 mA/cm2 at only 1.38 V. Compared to unmodified Ni(OH)2, the Pd/NiCo achieved an 8.3-fold increase in peak current density. DFT calculations and in-situ XAFS revealed that the Co sites affected the conformation and band structure of neighboring Ni sites through CoO6 octahedral distortion, reducing the proton deintercalation potential of Pd/NiCo and promoting the production of Ni3+-O active species accordingly. The involvement of Pd decreased the electronic transfer impedance, and thereby accelerated Ni3+-O formation. Moreover, the Pd clusters enhanced the adsorption of HMF through orbital hybridization, kinetically promoting the contact and reaction of HMF with Ni3+-O.

Pd Loaded NiCo Hydroxides for Biomass Electrooxidation: Understanding the Synergistic Effect of Proton Deintercalation and Adsorption Kinetics

AbstractThe key issue in the 5‐hydroxymethylfurfural oxidation reaction (HMFOR) is to understand the synergistic mechanism involving the protons deintercalation of catalyst and the adsorption of the substrate. In this study, a Pd/NiCo catalyst was fabricated by modifying Pd clusters onto a Co‐doped Ni(OH)2 support, in which the introduction of Co induced lattice distortion and optimized the energy band structure of Ni sites, while the Pd clusters with an average size of 1.96 nm exhibited electronic interactions with NiCo support, resulting in electron transfer from Pd to Ni sites. The resulting Pd/NiCo exhibited low onset potential of 1.32 V and achieved a current density of 50 mA/cm2 at only 1.38 V. Compared to unmodified Ni(OH)2, the Pd/NiCo achieved an 8.3‐fold increase in peak current density. DFT calculations and in situ XAFS revealed that the Co sites affected the conformation and band structure of neighboring Ni sites through CoO6 octahedral distortion, reducing the proton deintercalation potential of Pd/NiCo and promoting the production of Ni3+−O active species accordingly. The involvement of Pd decreased the electronic transfer impedance, and thereby accelerated Ni3+−O formation. Moreover, the Pd clusters enhanced the adsorption of HMF through orbital hybridization, kinetically promoting the contact and reaction of HMF with Ni3+−O.

Identifying A Universal Activity Descriptor and a Unifying Mechanism Concept on Perovskite Oxides for Green Hydrogen Production.

Producing indispensable hydrogen and oxygen for social development via water electrolysis shows more prospects than other technologies. Although electrocatalysts have been explored for centuries, a universal activity descriptor for both hydrogen-evolving (HER) and oxygen-evolving reactions (OER) has not been developed. Moreover, a unifying concept has not been established to simultaneously understand HER/OER mechanisms. Here, we rationally bridge the relationships between HER/OER activities in three common electrolytes and over 10 representative material properties on 12 3d-metal-based model oxides through statistical methodologies. Orbital charge-transfer energy (Δ) can serve as an ideal universal descriptor, where a neither too large nor too small Δ (∼1eV) with optimal electron-cloud density around Fermi level affords the best activities, fulfilling Sabatier's principle. Systematic experiments and computations unravel that pristine oxide with Δ ≈ 1eV possesses metal-like high-valence configurations and active lattice-oxygen sites to help adsorb key protons in HER and induce lattice-oxygen participation in OER, respectively. After reactions, partially generated metals in HER and high-valence hydroxides in OER dominate proton adsorption and couple with pristine lattice-oxygen activation, respectively. These can be successfully rationalized by the unifying orbital charge-transfer theory. This work provides the foundation of rational material design and mechanism understanding for many potential applications. This article is protected by copyright. All rights reserved.

Beneficial effect of copper on pitting resistance of Ni-Cr-Fe alloys

This study examines the effect of copper alloying on pitting resistance in a model solid solution FCC Ni-13%Cr-10%Fe alloy through potentiodynamic and potentiostatic polarization in 0.1 M NaCl in conjunction with an analysis using first-principles competitive electro-chemisorption modeling. The pitting potential increased with increasing Cu content in the alloy. Furthermore, the extent of metastable pit growth was suppressed and the incubation time for metastable to stable pit transition increased with Cu content. The first-principles competitive adsorption calculations suggested that Cu alloying suppresses chloride ion adsorption on the alloy surface in a simulated pit environment, which inhibits active dissolution at the pit bottom, enhances proton adsorption, and thereby increases the local pH at the pit bottom. We propose that these two effects of Cu in solid solution combine to reduce pit stability and may act in addition to the enrichment of Cu on the corroding pit surface.