Acid Electrolyte Research Articles

Electroanalytical Studies on Codeposition of Cobalt with Ruthenium from Acid Chloride Baths

The aim of this study was to systematically analyze the influence of potential and the Co(II)–Ru(III) molar ratio on the electrochemical behavior of the Co–Ru system during codeposition from acidic chloride electrolytes. The equilibrium speciation of the baths was investigated spectrophotometrically and compared with theoretical calculations based on the stability constants of Co(II) and Ru(III) complexes. The codeposition of the metals was characterized using electroanalytical methods, including cyclic voltammetry, chronoamperometry, and anodic stripping linear voltammetry. The alloys obtained at different potentials were analyzed for their elemental composition (EDS, mapping), phase composition (XRD), and surface morphology (SEM). The morphology and composition of the alloys were mainly dependent on the deposition potential, which controlled the cobalt incorporation. Ruthenium–rich alloys were produced at potentials of −0.6 V and −0.7 V (vs. SCE). In these conditions, cobalt anomalously codeposited due to the formation of the CoOH+ intermediate, triggered by the intense hydrogen evolution on the ruthenium sublayer. Bulk cobalt electrodeposition began at a potential of around −0.8 V, resulting in the formation of cobalt-rich alloys. The early stages of the electrodeposition were investigated using different nucleation models. A transition from 2D progressive nucleation to 3D instantaneous nucleation at around −0.8 V was identified as being caused by cobalt incorporation. This was well correlated with electroanalytical data, partial polarization curves of alloy deposition, elemental mapping analysis, and the structure of the deposits.

Composite electrochemical coatings of Ni-CrB2 from sulfuric acid and sulfamate electrolytes: formation, structure and properties

Electrodeposited coatings are in demand in many industries: due to the high adhesive strength to the base metal, they can be applied to complex-shaped products, and the thickness of the deposited coating can be controlled. However, standard electrolytic coatings do not always meet the necessary operating requirements. In this case, the formation of composite electrolytic coatings, which consist in the modification of electrolytes by various dispersed particles, becomes an urgent task. These particles are introduced into the electrolyte and deposited together with the precipitate metals, which leads to changes in the coating properties. In this article, the structure, adhesive and corrosion properties of nickel-chromium diboride composite coatings obtained in the electrodeposition process are studied. Precipitation was carried out in sulfuric acid and sulfamate electrolytes with a concentration of dispersed chromium diboride particles of 10-40 g/l. The coatings consist of nickel and CrB2 phases. The adhesive strength of the coating with a steel base is satisfactory; chipping and peeling were not observed. The corrosion resistance of sulfamate electrolyte coatings is higher than that of the coatings obtained from sulfuric acid electrolyte due to the compactness of nickel precipitates. Chromium diboride in the coating provides 1.5-2 times greater corrosion resistance.

High Efficiency Alkaline Iodine Batteries with Multi-Electron Transfer Enabled by Bi/Bi2O3 Redox Mediator.

The multi-electron transfer I-/IO3- redox couple is attractive for high energy aqueous batteries. Shifting from an acidic to an alkaline electrolyte significantly enhances the IO3- formation kinetics due to the spontaneous disproportionation reaction, while the alkaline environment also offers more favorable Zn anode compatibility. However, sluggish kinetics during the reduction of IO3- persists in both acidic and alkaline electrolytes, compromising the energy efficiency of this glorious redox couple. Here, we establish the fundamental redox mechanism of the I-/IO3- couple in alkaline electrolytes for the first time and propose that Bi/Bi2O3 acts as a redox mediator (RM) to "catalyze" the reduction of IO3-. This mediation significantly reduces the voltage gap between charge/discharge from 1.6 V to 1 V with improved conversion efficiency and rate capability. By pairing the Zn anode and the Bi/Bi2O3 RM cathode, the full battery with I-/IO3- redox mechanism achieves high areal capacity of 12 mAh cm-2 and stable operation at 5 mAh cm-2 for over 400 cycles.

Effect of Triton X-100 surfactant concentration on the wettability of polyethylene-based separators used in supercapacitors

Polyethylene-based separators are generally unsuitable for aqueous supercapacitors due to their poor wettability with the electrolyte, which impedes ion transport. However, incorporating Triton X-100 (2-[4-(2,4,4-trimethylpentan-2-yl)phenoxy]ethanol) into the aqueous sulfuric acid (H2SO4) electrolyte improves the wettability of polyethylene and facilitates ionic movement through its pores. In this study, Triton X-100 was added to 1.0 M H2SO4 at various concentrations (0.122%–1.210% V/V) to evaluate its impact on supercapacitor performance. Supercapacitors were assembled using activated carbon-filled carbon cloth electrodes, each of the above electrolytes and polyethylene sheet separators. Scanning electron microscopy revealed that the carbon cloth exhibited a uniform fiber distribution and high surface area for activated carbon integration. The polyethylene separator displayed a porous structure with an average pore size of 165 ± 35 nm. Triton X-100 significantly reduced the water contact angle from 101.5° (without surfactant) to 30.2° (with 1.21% V/V Triton X-100), enhancing polyethylene’s wettability. This change from hydrophobic to hydrophilic characteristics enabled the formation of an electrical double layer at the separator/electrolyte interface, improving ionic transport. However, higher Triton X-100 concentrations increased the electrolyte's viscosity, which impeded ion movement. The highest specific capacitance of 55.3 F/g (at a scan rate of 0.005 V s−1) was achieved with 0.488% V/V Triton X-100. The specific capacitance varied with surfactant concentration in a complex manner, influenced by micelle formation and precipitation. These findings were corroborated by cyclic voltammetry and AC impedance spectroscopy.

Acidic "Water-in-Salt" Electrolyte Enables a High-Energy Symmetric Supercapacitor Based on Titanium Carbide MXene.

Titanium carbide MXene, Ti3C2Tx, exhibits ultrahigh capacitance in acidic electrolytes at negative potentials yet poor stability at positive potentials, resulting in low-energy densities for Ti3C2Tx-based symmetric supercapacitors. Utilizing "water-in-salt" electrolytes has successfully expanded the stable operation potential window of MXenes. However, this advancement comes at the cost of sacrificing their high capacitance in acidic electrolytes. In this work, we report an acidic "water-in-salt" (AWIS) electrolyte composed of sulfuric acid and saturated lithium halide, which effectively doubled the energy density of the Ti3C2Tx-based symmetric supercapacitor compared to those with bare acidic electrolytes. Specifically, the AWIS electrolyte successfully expanded the voltage window of the symmetric device to 1.1 V. A high specific capacitance of 112.34 F g-1 (at 10 mV s-1) was obtained due to the presence of proton redox. As a result, the symmetric device achieved a high-energy density of 19.1 Wh kg-1 and a high capacitance retention of 96.3% after 10,000 cycles. This work demonstrates the importance of designing stable and redox-active electrolytes for high-energy MXene-based symmetric supercapacitors.

Toward the Rechargeable Aqueous Zinc Ion Batteries with Improved Overall Performance: Electrolyte with Surface Adsorptive Additive.

Aqueous zinc-ion batteries (AZIBs) with slightly acidic electrolytes process advantages such as high safety, competitive cost, and satisfactory electrochemical performance. However, the failure behaviors of both electrodes, regarding zinc dendrite growth, interfacial parasitic reactions, and the collapse of cathode materials hinder the practical application of ZIBs. To alleviate the issues of both anode and cathode at the same time, D-xylose (DX) is introduced to the electrolyte as a multifunctional additive. As a result, the side reaction of the anode is suppressed and the metallic deposition behavior is regulated due to the hydrogen bonding network reconstruction and preferential surface adsorption of DX; for the MnO2 cathode, the DX adsorption can help the interfacial charge transfer and increase the reactive sites. Benefiting from these merits, DX-optimized Zn//Zn battery displays reveal a prolonged lifespan of 6912h and an ultra-high cumulative capacity of 17.28Ahcm-2 at 5mAcm-2. With the function of water reactivity suppression, the Coulombic efficiency reaches 99.91% at 2mAcm-2; the Zn||MnO2 full batteries exhibit excellent cyclability over 2000 cycles at 5C with an increased capacity of 118.9mAhg-1, indicating the dual functions to both of the electrodes for AZIBs.

Sparkling Synergy: Enhancing Hydrogen Evolution with a Mesoporous CoP/FeP Interface.

The reaction kinetics is predominantly determined by the surface and interface engineering of electrocatalysts. Herein, we demonstrate the growth of cobalt monophosphide and iron monophosphide (CoP/FeP) with an effective solid interface. The surface of CoP/FeP is mesoporous, which is obtained by phosphidizing mesoporous CoFe2O4. The CoP/FeP electrode exhibits substantially superior hydrogen evolution reaction (HER) performance compared to CoP and FeP. The overpotentials (η) required to generate 10 mA cm-2 are determined to be around 98 mVRHE (CoP/FeP), 220 mVRHE (FeP), and 265 mVRHE (CoP) in an acidic electrolyte. The exchange current density and Tafel slopes suggest that CoP/FeP has better redox properties and kinetic abilities compared to FeP and CoP. Furthermore, the CoP/FeP electrode exhibits reduced electrochemical impedance and superior surface charge transport characteristics in comparison to both the CoP and FeP electrodes. In addition to having a greater number of catalytically active sites, the turnover frequency of CoP/FeP is approximately 2 and 5 times higher than that of FeP and CoP, respectively. The CoP/FeP electrode maintains a consistent current density of around 25 mA cm-2 for a continuous period of 24 h during the HER, attesting to the excellent durability of the CoP/FeP electrode. In addition, a relationship between differential hydrogen adsorption energy (ΔEH), the corresponding Gibbs free energy change (ΔGH), and the hydrogen coverage on distinct surfaces, namely, CoP, FeP, and CoP/FeP, is established. The calculation findings show that the CoP/FeP surface, which is predominantly exposed with CoP, exhibits the highest catalytic potential for the HER. The estimation of the specific HER activity of the electrodes, normalized to the electrochemically active surface area, corroborates the calculation findings.

Capacitive behaviors for surface-sulfonated polyaniline nanofibers in different acidic electrolytes

Abstract Unique surface-sulfonated polyaniline nanofibers (PANI-S) were fabricated through one-pot polymerization to evaluate the feasibility of their applications as electrode materials for high-performance supercapacitors that can be operated in relatively weak acidic electrolytes. Benefiting from the self-doping effect and improved dispersion in aqueous solution for the nanofibers, as well as the effective buffering function of the electrolyte, the PANI-S exhibits excellent capacitive performance across a broad pH value range in acidic electrolytes. More clearly, the specific capacitance of the PANI-S remains remarkably stable, ranging from 752.4 to 754.4 F g−1 at a scan rate of 5 mV s−1 and from 575.4 to 536.8 F g−1 at a current density of 1 A g−1, as the pH value of the electrolyte varies from 0 to 6. However, the capacity retention rate of PANI-S gradually decreases from 79.2% to 37.2% as the current density increases from 1 A g−1 to 20 A g−1, with the pH of the buffered solution increasing from 0 to 6. The excellent electrochemical activity in low acidic electrolytes for PANI nanofibers can be attributed to the compensation effects of the self-doped local proton reservoir.

Ruthenium Single-Atom Modulated Protonated Iridium Oxide for Acidic Water Oxidation in Proton Exchange Membrane Electrolysers.

Proton exchange membrane water electrolysers promise to usher in a new era of clean energy, but they remain a formidable obstacle in designing active and durable electrocatalysts for the acidic oxygen evolution reaction (OER). In this study, a protonated iridium oxide embedded with single-atom dispersed ruthenium atoms (H3.8Ir1- xRuxO4) that demonstrates exceptional activity and stability in acidic water oxidation is introduced. The single Ru dopants favorably induce localized oxygen vacancies in the Ir─O lattice, synergistically strengthening the adsorption of OOH* intermediates and enhancing the intrinsic OER activity. In addition, the preferential oxidation of Ru and the electronegativity of the oxygen vacancies significantly stabilize the Ir─O active sites, improving the OER stability. Consequently, the H3.8Ir1─ xRuxO4 catalyst shows an overpotential of 255mV at 10mA cm-2 and displays exceptional catalytic endurance in acidic electrolytes, surpassing 1100 h, representing a remarkable one-order-of-magnitude increase in stability compared to that of pristine H3.8IrO4. A proton exchange membrane electrolyser utilizing the H3.8Ir1- xRuxO4 catalyst as an anode exhibits stable performance for more than 1280 h under a high current density of 2 A cm-2.

Evaluation of wear and corrosion resistance in acidic and chloride solutions of Cathodic Arc PVD chromium nitride coatings on untreated and plasma nitrided AISI 4140 steel

Chromium nitride ceramic like coatings are well known for their hardness and wear resistance, especially under severe conditions. When deposited on mild steel, nitriding is required for such applications to create a gradient hardness profile and improve the coating adhesion and the system's mechanical properties. Corrosion resistance is also necessary since these chromium coatings are recommended for applications in the plastic mould and injection industry. Therefore, in this work, the combination of a nitriding without white layer pretreatment and CrN coating was studied in a chloride and an acidic electrolyte, to asses if the diffusion layer also plays an important role as a corrosion protection treatment. Coating microstructure, adhesion to both nitrided and non-nitrided steel, wear resistance, and corrosion resistance in chloride and acidic media were evaluated. For comparison, bare and nitrided steel were also examined. Results indicated an improvement in the adhesion for the duplex treatment (nitriding + CrN). The CrN coating demonstrated a considerably lower coefficient of friction and wear rate compared to both non-nitrided and nitrided steel. Regarding corrosion, the iron nitride layer provides some protection in chloride environments; however, in acidic media, only the CrN coating plays a protective role. In both media, localized attack occurred at sites where the coating had defects, such as pores or pinholes through which the electrolyte comes into contact with the substrate. The duplex treatment proved to be the most effective surface treatment for AISI 4140, achieving excellent tribological properties, good adhesion, and high corrosion resistance in both neutral chloride and acidic solutions.

Strategically Modulating Proton Activity and Electric Double Layer Adsorption for Innovative All-Vanadium Aqueous Mn2+/Proton Hybrid Batteries.

Aqueous Mn-ion batteries (MIBs) exhibit a promising development potential due to their cost-effectiveness, high safety, and potential for high energy density. However, the development of MIBs is hindered by the lack of electrode materials capable of storing Mn2+ ions due to acidic manganese salt electrolytes and large ion radius. Herein, the tunnel-type structure of monoclinic VO2 nanorods to effectively store Mn2+ ions via a reversible (de)insertion chemistry for the first time is reported. Utilizing exhaustive in situ/ex situ multi-scale characterization techniques and theoretical calculations, the co-insertion process of Mn2+/proton is revealed, elucidating the capacity decay mechanism wherein high proton activity leads to irreversible dissolution loss of vanadium species. Further, the Grotthuss transfer mechanism of protons is broken via a hydrogen bond reconstruction strategy while achieving the modulation of the electric double-layer structure, which effectively suppresses the electrode interface proton activity. Consequently, the VO2 demonstrates excellent electrochemical performance at both ambient temperatures and -20°C, especially maintaining a high capacity of 162mAhg-1 at 5Ag-1 after a record-breaking 20000 cycles. Notably, the all-vanadium symmetric pouch cells are successfully assembled for the first time based on the "rocking-chair" Mn2+/proton hybrid mechanism, demonstrating the practical application potential.

Investigating Layered Topological Magnetic Materials as Efficient Electrocatalysts for the Hydrogen Evolution Reaction under High Current Densities

Despite considerable progress, high-performing durable catalysts operating under large current densities (i.e., >1000 mA/cm2) are still lacking. To discover platinum group metal-free (PGM-free) electrocatalysts for sustainable energy, our research involves investigating layered topological magnetic materials (semiconducting ferromagnets) as highly efficient electrocatalysts for the hydrogen evolution reaction under high current densities and establishes the novel relations between structure and electrochemical property mechanisms. The materials of interest include transition metal trihalides, i.e., CrCl3, VCl3, and VI3, wherein a structural unit, the layered structure, is formed by Cr (or V) atoms sandwiched between two halides (Cl or I), forming a tri-layer. A few layers of quantum crystals were exfoliated (~50−60 nm), encapsulated with graphene, and electrocatalytic HER tests were conducted in acid (0.5M H2SO4) and alkaline (1M KOH) electrolytes. We find a reasonable HER activity evolved requiring overpotentials in a range of 30–50 mV under 10 mA cm−2 and 400−510 mV (0.5M H2SO4) and 280−500 mV (1M KOH) under −1000 mA cm−2. Likewise, the Tafel slopes range from 27 to 36 mV dec−1 (Volmer–Tafel) and 110 to 190 mV dec−1 (Volmer–Herovsky), implying that these mechanisms work at low and high current densities, respectively. Weak interlayer coupling, spontaneous surface oxidation, the presence of a semi-oxide subsurface (e.g., O–CrCl3), intrinsic Cl (or I) vacancy defects giving rise to in-gap states, electron redistribution (orbital hybridization) affecting the covalency, and sufficiently conductive support interaction lowering the charge transfer resistance endow the optimized adsorption/desorption strength of H* on active sites and favorable electrocatalytic properties. Such behavior is expedited for bi-/tri-layers while exemplifying the critical role of quantum nature electrocatalysts with defect sites for industrial-relevant conditions.

Hierarchical porous MXene film with diffusion path optimization for supercapacitor

MXenes have immense potential in electrochemical energy storage owing to their outstanding physicochemical properties such as their oxygen-containing groups that impart additional pseudocapacitance to acidic electrolytes. However, during electrode assembly, MXene nanosheets undergo restacking because of hydrogen bonding and van der Waals forces, which causes electrolyte ions to traverse long diffusion pathways between the long and narrow nanosheets. Exploiting the oxidative properties of Ti3C2Tx, a hierarchical porous MXene film with micro-, meso- and macroporous structures was successfully prepared using a simple hydrothermal oxidation and etching process to create micro- and mesoporous structures, followed by ice templating to prepare three-dimensional (3D) linked macroporous structures. Because these hierarchical pores have synergistic effects on electrochemical activity and electrolyte ion diffusion, the film attained a specific capacitance of 539F/g at a current density of 2 A/g when it was used as a supercapacitor electrode, which corresponds to one of the highest values reported for MXene-based electrodes. The film retained 83% of its specific capacitance when the current density was increased to 40 A/g, and exhibited excellent cycling stability. By using this multi-porous MXene design, synergistic improvement in ion diffusion was successfully realized and thus a new strategy to prepare high-performance supercapacitor electrode materials was developed.

Optimal Electrocatalyst Design Strategies for Acidic Oxygen Evolution.

Hydrogen, a clean resource with high energy density, is one of the most promising alternatives to fossil. Proton exchange membrane water electrolyzers are beneficial for hydrogen production because of their high current density, facile operation, and high gas purity. However, the large-scale application of electrochemical water splitting to acidic electrolytes is severely limited by the sluggish kinetics of the anodic reaction and the inadequate development of corrosion- and highly oxidation-resistant anode catalysts. Therefore, anode catalysts with excellent performance and long-term durability must be developed for anodic oxygen evolution reactions (OER) in acidic media. This review comprehensively outlines three commonly employed strategies, namely, defect, phase, and structure engineering, to address the challenges within the acidic OER, while also identifying their existing limitations. Accordingly, the correlation between material design strategies and catalytic performance is discussed in terms of their contribution to high activity and long-term stability. In addition, various nanostructures that can effectively enhance the catalyst performance at the mesoscale are summarized from the perspective of engineering technology, thus providing suitable strategies for catalyst design that satisfy industrial requirements. Finally, the challenges and future outlook in the area of acidic OER are presented.

Enhanced solar hydrogen evolution by laminated integration of n+p-SiIP/TiO2/Pt inverted pyramid black Si photocathode

The nano/microstructuring of silicon (Si) via chemical methods has garnered significant attention due to its excellent light-trapping capabilities across a wide spectral range. Current research has predominantly focused on the synthesis of pyramidal-shaped microtextures, which enable two reflections on the surface, while largely overlooking the superior light-trapping potential of inverted pyramid silicon (SiIP) microtextures, which theoretically allow for three reflections. Moreover, there has been limited investigation into the application of inverted pyramid black silicon for solar-driven hydrogen evolution. This study reports the synthesis of uniformly arranged inverted pyramid-textured black silicon using the copper-assisted chemical etching (Cu-ACE) method to enhance the efficiency of solar-driven water splitting for hydrogen production. The formation mechanism and the influence of copper-localized surface plasmon resonance (Cu-LSPR) from Cu nanoparticle (NP) byproducts on photoelectrochemical (PEC) activity were systematically analyzed. To reduce sidewall defects and minimize photogenerated carrier recombination, the surface of the SiIP was treated with tetramethylammonium hydroxide (TMAH). A vertical PN junction was developed through ion implantation to reduce the external bias of the SiIP. Additionally, a uniform TiO₂ antireflective layer was deposited via atomic layer deposition (ALD), reducing the average reflectance of the SiIP-T4 to 5.78 % over the 300–1100 nm wavelength range. MoSₓ and Pt NPs were electrodeposited to improve the fill factor and enhance HER kinetics. With optimized catalyst loading, the n+p-SiIP-T4/TiO₂/Pt 80 mC electrode achieved a photocurrent density of 8.0 mA cm−2 at 0 V vs. RHE, an applied bias photon-to-current efficiency (ABPE) of 0.93 % at 0.24 V vs. RHE, and a double-layer capacitance (Cdl) of 91 μF cm−2. The onset potential (Von) was positively shifted by ∼1.13 V to 0.49 V vs. RHE compared to a SiIP photocathode, and the photocathode operated continuously at 0 V vs. RHE for 27 h in an acidic electrolyte. These results demonstrate that SiIP has significant potential for PEC hydrogen evolution, with further performance optimization achievable through structural and surface engineering.

Advanced Dual‐Band Smart Windows: Inorganic All‐Solid‐State Electrochromic Devices for Selective Visible and Near‐Infrared Modulation

AbstractDual‐band electrochromic smart windows (DESWs), capable of actively and selectively modulate visible (VIS) light and near‐infrared (NIR) heat, have emerged as a practical technology for enhancing user comfort and reducing building energy consumption. However, the design and development of DESWs remain a significant challenge due to the difficulty in obtaining suitable materials and high‐durability electrolytes. Here, the first all‐solid‐state DESW based on an orthorhombic oxygen‐deficient tungsten oxide (o‐WO3‐x) film is presented. Benefiting from the synergistic effects of the efficient oxygen‐vacancy‐enhanced charge transfer process and the secure transfer pathway enabled by the orthorhombic crystal structure, the o‐WO3‐x film showcases remarkable dual‐band electrochromic properties, including selective modulation of VIS light and NIR heat, large optical modulation (89.1%), rapid response time (tb/tc = 6.8/17.9 s), high coloration efficiency (155.92 cm2 C−1), and ultrastable cyclic performance (8000 cycles) even in acidic aqueous electrolyte. Furthermore, the all‐solid‐state DESWs incorporating o‐WO3‐x deliver a significant and stable dual‐band electrochromic response with excellent thermal regulation and energy‐saving capabilities. These findings underscore the considerable potential of o‐WO3‐x films and their all‐solid‐state smart windows in decreasing building energy consumption.

Topologically Close-Packed Frank-Kasper C15 Phase Intermetallic Ir Alloy Electrocatalysts Enables High-Performance Proton Exchange Membrane Water Electrolyzer.

Chemical synthesis of unconventional topologically close-packed intermetallic nanocrystals (NCs) remains a considerable challenge due to the limitation of large volume asymmetry between the components. Here, a series of unconventional intermetallic Frank-Kasper C15 phase Ir2M (M = rare earth metals La, Ce, Gd, Tb, Tm) NCs is successfully prepared via a molten-salt assisted reduction method as efficient electrocatalysts for hydrogen evolution reaction (HER). Compared to the disordered counterpart (A1-Ir2Ce), C15-Ir2Ce features higher Ir-Ce coordination number that leads to an electron-rich environment for Ir sites. The C15-Ir2Ce catalyst exhibits excellent and pH-universal HER activity and requires only 9, 16, and 27mV overpotentials to attain 10mA cm-2 in acidic, alkaline, and neutral electrolytes, respectively, representing one of the best HER electrocatalysts ever reported. In a proton exchange membrane water electrolyzer, the C15-Ir2Ce cathode achieves an industrial-scale current density of 1 A cm-2 with a remarkably low cell voltage of 1.7V at 80°C and can operate stably for 1000 h with a sluggish voltage decay rate of 50 µV h-1. Theoretical investigations reveal that the electron-rich Ir sites intensify the polarization of *H2O intermediate on C15-Ir2Ce, thus lowering the energy barrier of the water dissociation and facilitating the HER kinetics.

The Electrode/Electrolyte Interface Study during the Electrochemical CO2 Reduction in Acidic Electrolytes.

Electrochemical CO2 Reduction (CO2R) in acidic electrolytes has gained significant attention owing to higher carbon efficiency and stability than in alkaline counterparts. However, the proton source and the role of alkali cations for CO2R are still under debate. By using rotating ring disk electrode and surface-enhanced infrared absorption spectroscopy, we find that a neutral/alkaline environment at the interface is necessary for CO2R even in acidic electrolytes. We also confirm that water molecules, rather than protons serve as the proton source for CO2R. Alkali cations in the outer Helmholtz plane activate H2O and promote the desorption of adsorbed carbon monoxide. Additionally, the solvated CO2, or CO2(aq), is the actual reactant for CO2R. This study provides a deeper understanding of the electrode/electrolyte interface during CO2R in acidic electrolytes and sheds light on further performance improvement of this system.

The Electrode/Electrolyte Interface Study during the Electrochemical CO2 Reduction in Acidic Electrolytes

The Electrode/Electrolyte Interface Study during the Electrochemical CO2 Reduction in Acidic Electrolytes

Ionic liquid-assisted controlled synthesis of multi-site Ni2P as a bifunctional catalyst for electrocatalytic water splitting

It is crucial to develop effective electrocatalysts with multiple active sites for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in order to promote the advance energy conversion and development of sustainable energy technology. Here, we synthesized hierarchical nanostructured Ni2P on carbon cloth using ionic liquid (IL) assisted sacrificial template strategy through a simple two-step hydrothermal phosphatization process, which served as an electrode for enhancing bifunctional water electrolysis. By changing the content of ionic liquids in the solvent, the morphology of Ni(OH)2 precursors could be regulated, thereby altering the morphology of Ni2P. Ni2P exhibited remarkable electrocatalytic activity towards HER in acidic electrolytes with an overpotential of 132 mV at a current density of 10 mA cm−2, as well as OER in alkaline media with the overpotential of 309 mV. The excellent electrocatalytic activity of the Ni2P-2 could be attributed to its hierarchical nanostructure providing abundant active sites, which benefits from the structural end-capping effect of ILs.