Water Splitting Reaction Research Articles

Surface Reconstruction Facilitated by Fluorine Migration and Bimetallic Center in NiCo Bimetallic Fluoride Toward Oxygen Evolution Reaction.

Oxygen evolution reaction (OER) is a critical anodic reaction of electrochemical water splitting, developing a high-efficiency electrocatalyst is essential. Transition metal-based catalysts are much more cost-effective if comparable activities can be achieved. Among them, fluorides are rarely reported due to their low aqueous stability of coordination and low electric conductivity. Herein, a NiCo bimetallic fluoride with good crystallinity is designed and constructed, and significantly enhanced catalytic activity and conductivity are observed. The inevitable oxidation of transition metal ions at high potential and the dissociation of F- are attributed to the low aqueous stability of coordination. The theoretical researches predicte that transition metal fluorides should have a strong tendency to electrochemical reconstruction. Therefore, based on the observations on their electrochemical behavior, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and bode plots, it is further demonstrated that surface reconstruction occurred during the electrochemical process, meanwhile a significant increase of electrochemically active area, which is created by F migration, are also directly observed. Additionally, DFT calculation results show that the electronic structure of the catalysts is modulated by the bimetallic centers, and this reconstruction helps optimizing the adsorption energy of oxygen-containing species and improves OER activity.

Metal–organic framework and carbon hybrid nanostructures: Fabrication strategies and electrocatalytic application for the water splitting and oxygen reduction reaction

Metal–organic framework and carbon hybrid nanostructures: Fabrication strategies and electrocatalytic application for the water splitting and oxygen reduction reaction

A Mathematical Model for the Membrane Electrode Assembly of a Bicarbonate Electrolyzer

Bicarbonate electrolyzers are devices designed to convert CO2 released in situ from bicarbonate ions into chemicals and fuels without an external source of CO2 gas. A one-dimensional steady-state isothermal model is developed for the membrane electrode assembly of a bicarbonate CO2 electrolyzer with a bipolar membrane design. The model incorporates species transport in both the anode and cathode electrodes due to convection, diffusion, and migration, and accounts for the catalyzed water splitting reaction at the interface of the anion exchange layer and the cation exchange layer of the bipolar membrane. A direct comparison of model simulations with available experimental data shows that the model can accurately simulate measured Faradaic efficiency and CO yield for all operating current densities. The model can also accurately simulate most of the polarization curve, with the only limitation being in the range dominated by mass transport. Compared to the other parameters studied in this paper, numerical results show that the performance of the bicarbonate CO2 electrolyzer is more sensitive to both aqueous electrolyte saturation in the cathode catalyst layer and the catalyzed water splitting efficiency of the bipolar membrane.

A computational study photophysical properties of a series phenothiazine-linked-BODIPY as D-D-π-a photosensitizer unit for photo-induced hydrogen production from water

Phenothiazine-derivatives are designed as sensitizers which covalently-linked with BODIPY for application in a system of dye-sensitized photoelectrochemical cells (DSPECs). A series of phenothiazine-linked-BODIPY as D-D-π-A chromophore have been investigated by a computational approach for studying the capability of the photosensitizers for application in photoinduced water splitting hydrogen production in DSPECs. The geometries of sensitizers at the ground state and excited state were optimized by the CAM-B3LYP/6-31G (d,p) level method. The theoretical study has been done in order to investigate the photophysical properties such as absorption profile, HOMO-LUMO energy and surface plots of the photosensitizer. The result of calculation for HOMO-LUMO energy level of each dyes showed that the LUMO energy are ranging more than -2.8 - (-2.86) eV which is higher than -4.0 eV of conduction band of TiO2 as semiconductor in DSPEC, meaning that all these dyes could be used as photosensitizers in DSPECs. In addition, the oscillator strength data of each dyes showed the dyes have absorption profile in visible region, meaning the dyes could harvest higher intensity of sunlight to induce water splitting reaction to produce hydrogen.

One-Step Dry Coating of Hybrid ZnO-WO3 Nanosheet Photoanodes for Photoelectrochemical Water Splitting with Composition-Dependent Performance.

In this study, the potential of zinc oxide (ZnO), tungsten oxide (WO3), and their composites (ZnO-WO3) as photoanodes for photoelectrochemical (PEC) water splitting was investigated. ZnO-WO3 nanocomposites (NCs) were deposited on fluorine-doped tin oxide substrates at room temperature using a one-step dry coating process, the nanoparticle deposition system, with no post-processes. Different compositions of ZnO-WO3 NCs were optimized to enhance the kinetics of the PEC water-splitting reaction. Surface morphology analysis revealed the transformation of microsized particle nanosheets (NS) powder into nanosized particle nanosheets (NS) across all photoanodes. The optical characteristics of ZnO-WO3 photoanodes were scrutinized using diffuse reflectance and photoluminescence emission spectroscopy. Of all the hybrid photoanodes tested, the photoanode containing 10 wt.% WO3 exhibited the lowest bandgap of 3.20 eV and the lowest emission intensity, indicating an enhanced separation of photogenerated carriers and solar energy capture. The photoelectrochemical results showed a 10% increase in the photocurrent with increasing WO3 content in ZnO-WO3 NCs, which is attributed to improved charge transfer kinetics and carrier segregation. The maximum photocurrent for a NC, i.e., 10 wt.% WO3, was recorded at 0.133 mA·cm-2 at 1.23V vs. a reversible hydrogen electrode (RHE). The observed improvement in photocurrent was nearly 22 times higher than pure WO3 nanosheets and 7.3 times more than that of pure ZnO nanosheets, indicating the composition-dependence of PEC performance, where the synergy requirement strongly relies on utilizing the optimal ZnO-WO3 ratio in the hybrid NCs.

Highly efficient water-splitting electrodes with stable operation at 3 A cm−2 in alkaline media through molecular linker assembly-induced all-in-one structured NiMo and NiFe electrocatalysts

Developing nonnoble electrocatalyst-based water-splitting electrodes with high operational stability and low overpotentials is one of the most critical challenges in commercially available water-splitting reactions. In this study, we present water-splitting textile electrodes enabling remarkably low overpotentials and high stable operation. We first assembled conductive multi-walled-carbon-nanotubes (MWCNTs) with amine molecule-based linkers onto cotton textiles and subsequently electrodeposited Ni onto the MWCNT-incorporated textile. For the preparation of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrodes, NiMo and NiFe were further electrodeposited onto the Ni-electrodeposited textile electrode, respectively. These electrodes exhibited considerably low overpotentials in alkaline media (8 mV at 10 mA cm−2 for HER and 189 mV at 50 mA cm−2 for OER). Furthermore, the full-cell electrodes preserved a low cell voltage of 2.01 V at an unprecedentedly high current density of 3000 mA cm−2 for a prolonged duration (> at least 1000 h).

Stable and wide spectrum response Zn3As2/Al2O3 photocatalyst for photocatalytic overall water splitting

Constructing highly efficient and durable non-noble-metal photocatalysts with a broad spectral response for promoting sluggish photocatalyticover water splitting reaction is very desirable but still challenging. To realize scalable hydrogen production, an energy conversion efficiency of 10 % and stable photocatalysts with broad light-absorption are required. To this end, a wide spectrum response Zn3As2/Al2O3 has been successfully synthesized by a layer-by-layer coating method as a photocatalyst utilized in the hydrogen evolution reaction (HER) for the first time, which gave the HER rate of 92.5 μmol·g−1·h−1. The HER activity did not decline obviously after three runs. Characterization results and photocatalytic performance confirmed that the Al2O3 layer could protect Zn3As2 from photocorrosion, which exhibited preeminent stability and outstanding photocatalytic performance. In addition, Zn3As2/Al2O3 showed light response extending to ∼1300 nm, and more efficient separation capability of photogenerated charges benefited from the built-in electric field between Al2O3 and Zn3As2, which were verified by UV–Vis–NIR DRS and electrochemical measurements. Our research results may provide a new route of design and construction of stable and efficacious photocatalysts to realize solar energy conversion to hydrogen.

Enhanced Visible Light-Driven Photocatalytic Water-Splitting Reaction of Titanate Nanotubes Sensitised with Ru(II) Bipyridyl Complex.

The ion exchange of Na+ cations was used to photosensitise titanates nanotubes (Ti-NTs) with tris(2,2'-bipyridine)ruthenium(II) cations (Ru(bpy)32+); this yielded a light-sensitised Ti-NTs composite denoted as (Ru(bpy)3)Ti-NTs, exhibiting the characteristic absorption of Ru(bpy)32+ in visible light. Incident photon-to-current efficiency (IPCE) measurements and the photocatalytic reduction of methyl viologen reaction confirmed that in the photosensitisation of the (Ru(bpy)3)Ti-NTs composite, charge transfer and charge separation occur upon excitation by ultraviolet and visible light irradiation. The photocatalytic potential of titanate nanotubes was tested in the water-splitting reaction and the H2 evolution reaction using a sacrificial agent and showed photocatalytic activity under various light sources, including xenon-mercury lamp, simulated sunlight, and visible light. Notably, in the conditions of the H2 evolution reaction when (Ru(bpy)3)Ti-NTs were submitted to simulated sunlight, they exceeded the photocatalytic activity of pristine Ti-NTs and TiO2 by a factor of 3 and 3.5 times, respectively. Also, (Ru(bpy)3)Ti-NTs achieved the photocatalytic water-splitting reaction under simulated sunlight and visible light, producing, after 4 h, 199 and 282 μmol×H2×gcat-1. These results confirm the effective electron transfer of Ru(bpy)3 to titanate nanotubes. The stability of the photocatalyst was evaluated by a reuse test of four cycles of 24 h reactions without considerable loss of catalytic activity and crystallinity.

Escalating the synergism on CdZnS via Ag2S/Cu2S co-catalysts: Boosts hydrogen evolution from water splitting under sunlight

Photocatalytic hydrogen production through water splitting is one of the effective ways to fulfill future energy demands. In current study, Ag and Cu were simultaneously incorporated into CdZnS through hydrothermal reaction to synthesize 1 % Ag2S/Cu2S codoped-CdZnS. The catalysts were characterized via XRD, FT-IR, SEM, EDX, UV–Vis/DRS, XPS, BET, PL and EIS techniques. It has been observed that 1 % Ag2S/Cu2S is optimized amount of dopants that enables CdZnS to produce hydrogen with 9.76 mmol g−1h−1 rate. This amount of H2 is 3 times higher than that of bare CdZnS (2.91 mmol g−1h−1). Photocatalytic activity shown by 1 % Ag2S/Cu2S-CdZnS is due the incorporation of Ag and Cu which exist in the form of Ag2S and Cu2S clusters respectively and causes synergistic effect during photoreaction. During the photoreactions, oxidation half reactions occur at Ag2S, while reduction half reaction at Cu2S (i.e. conversion of H+ ions to H2). On the basis of the results, it can be concluded that Cu2S acts as reduction co-catalyst while Ag2S serves as oxidation co-catalyst in water reduction reaction. This work could offer efficient and low cost photocatalysts for hydrogen production from the water splitting reactions.

Co/Ni-MOF as a bifunctional electrode material for electrochemical sensor and oxygen evolution reaction

In recent years, the demand for economical multifunctional materials has increased significantly. In this paper, Co/Ni-based bimetallic-organic frameworks (Co/Ni-MOFs) materials were prepared, which showed good electrochemical recognition and oxygen evolution bifunctional activity in alkaline environment. The electrochemical test showed that the response time of the material to glucose was less than 3 s, the sensitivity was 2.0826 μAmM−1 cm−2, and the detection limit was 8.84 μM. The material also exhibits a good overpotential of 410 mV at a current density of 100 mA cm−2 and Tafel slope of 451 mV dec−1. The results show that Co/Ni-MOFs can be used as an electrocatalyst for electrochemical sensors and water splitting reactions.

Amorphous high-entropy IrRuCrFeCoNiOx as efficient water splitting oxygen evolution reaction electrocatalysts

The process of oxygen evolution reaction (OER) for water splitting is intricate and demands a substantial amount of energy. It necessitates the utilization of catalysts that are both highly efficient and durable in order to overcome the slow reaction kinetics. Amorphous, high-entropy oxide nanoparticles were prepared using simple one-step coprecipitation in this work. Due to highly disordered atomic arrangement in the amorphous structure of these catalysts and their high specific surface area, they compete to form active sites in the OER. Among them, IrRuCrFeCoNiOx demonstrated the optimal OER catalytic activity, requiring just a low overpotential (190 mV) with minimal Tafel slope (51.1 mV dec−1) to achieve the current density of 10 mA cm−2 in 1 M KOH. Through surface self-reconstruction in the OER, a crystalline active layer with a thickness of several nanometers formed on the catalyst’s surface. The stable core-shell nanoarchitectures composed of crystalline and amorphous regions substantially improved the stability of the catalyst. This work verified the effectiveness of high-entropy design and the significant improvement of noble metal doping on OER performance. It develops a new OER catalyst for water splitting with great activity and stability.

Pulsed laser ablation synthesis of Cu-based and Ni-based nanostructured electrodes for highly active alkaline oxygen and hydrogen evolution reactions

In the field of sustainability, hydrogen (H2) is considered a clean fuel and a renewable energy source with no pollutant emissions. The production of H2 by water electrolysis is well-known among the scientific community. Still, alkaline electrolysis represents a challenging process and requires expensive materials have to be avoided in order to lower the impact of H2 production. This work deals with the production of copper (Cu) and nickel (Ni) nanoparticles (NPs) as catalysts for alkaline water splitting reactions. These NPs are synthesized using the pulsed laser ablation in liquid involving the ablation of Cu and Ni targets in methanol and ethanol. The morphological, structural, and compositional properties of the obtained NPs are studied. Then, a low amount of NPs-based catalyst (∼1μg/cm2) was loaded onto a nickel foam substrate and tested for both alkaline Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER). The best performance at 10 mA cm−2, in terms of overpotential (η), for OER was shown by Ni NPs, η = 327 mV, while for the HER, Cu NPs reached η = 211 mV at 10 mA cm−2 in aqueous 1M KOH. The ultra-low amount of the catalyst material makes these electrodes challenging in terms of mass activity [up to 14 A/mg at 10 mA cm−2] compared to the state of the art. In addition, the correlation between overpotential and the availability of electrons at the surface of the catalyst for H2 production was studied by using Mott–Schottky analysis.

Sulfur/Nitrogen-Codoped Carbon-Dot-Modified WO3 Nanosheets toward Enhanced Charge-Carrier Separation in a Saline Water-Splitting Reaction

Sulfur/Nitrogen-Codoped Carbon-Dot-Modified WO₃ Nanosheets toward Enhanced Charge-Carrier Separation in a Saline Water-Splitting Reaction

Optical Interactions in Bio-Electricity Generation from Photosynthesis in Microfluidic Micro-Photosynthetic Power Cells

Within the realm of renewable energy sources, biological-based power systems have emerged as pivotal players particularly suited for low- and ultra-low-power applications. Unlike microbial fuel cells (MFCs), which invariably rely on external carbon feedstock, micro-photosynthetic cells (µPSCs) exhibit a unique feature by operating independently of organic fuel. They harness the principles of photosynthesis and respiration to generate electricity in both illuminated and dark settings through water-splitting reactions. Here, we present a viable, easy, and cost-effective method to fabricate µPSCs. We meticulously examined the performance of a fabricated µPSC under varying illuminations and even in the absence of light. With an electrode surface area spanning 4.84 cm2, the µPSC achieved its peak power output of 200.6 µW when exposed to an illumination of 2 µmolm−2s−1 (equivalent to 147 lux). Of the three light intensities studied, 2 µmolm−2s−1, 8 µmolm−2s−1 (595 lux), and 20 µmolm−2s−1 (1500 lux), the µPSC exhibited its optimal performance at a light intensity of 2 µmolm−2s−1, establishing this as the ideal operational illumination. Furthermore, intermittent toggling of the illumination had no discernible impact on the µPSC’s performance. However, subjecting it to a dark environment for 30 min resulted in a reduction in the maximum power to 81 µW, marking a significant 119% decrease when compared to the peak power output achieved under 2 µmolm−2s−1 illumination.

Distinctive graphdiyne coupled with phosphorylation NiFe-LDH S-scheme heterojunction for photocatalytic overall water splitting

Most of the photocatalytic reactions currently involved require the use of precious metals or sacrificial reagents to achieve more desirable reactivity and stability. It is urgent to find low-cost photocatalysts that can be stable overall pure water splitting with high efficiency. Graphdiyne (GDY), as the youngest member of the carbon family, has received extensive attention in numerous fields. Herein, the innovative strategy of S-scheme heterojunction composite photocatalysts use to heterogeneous catalysis produce of H2 and H2O2 from photocatalytic pure water splitting is designed using of graphdiyne (GDY) and phosphorylation NiFe layered double hydroxide (NiFe-P). The electron transfer mechanism of S-scheme heterojunction catalyst was verified with in-situ irradiation X-ray photoelectron spectroscopy and hydroxyl radical capture experiments. Achieving multiphase catalysis in pure water, the hydrogen production rate reached 928 μmol h-1g−1, and the H2O2 production rate reached 674 μmol h-1g−1. This work provides new effective scheme for studying the charge transfer pathway of S-scheme heterojunction and feasible methods for constructing efficient photocatalytic-driven pure water splitting reactions.

Surface/Interface Engineering of Hierarchical MoO2/MoNi4@Ru/RuO2 Heterogeneous Nanosheet Arrays for Alkaline Water Electrolysis with Fast Kinetics

Comprehensive SummaryRealizing the hydrogen economy by water electrolysis is an attractive approach for hydrogen production, while the efficient and stable bifunctional catalysts under high current densities are the bottleneck that limits the half‐cell reactions of water splitting. Here, we propose an approach of hydrothermal and thermal annealing methods for robust MoO2/MoNi4@Ru/RuO2 heterogeneous cuboid array electrocatalyst with multiplying surface‐active sites by depositing a monolayer amount of Ru. Benefiting from abundant MoO2/MoNi4@Ru/RuO2 heterointerfaces, MoO2/MoNi4@Ru/RuO2 heterogeneous cuboid array electrocatalysts effectively drive the alkaline water splitting with superior hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances. The synthesized MoO2/MoNi4@Ru/RuO2 has high HER activity, which realizes the working overpotentials of 48 mV at 50 mA·cm–2, further achieving overpotentials of 230 mV for industry‐level 1000 mA·cm–2 in alkaline water electrolysis. Moreover, it also showed an enhanced OER activity than commercial RuO2 with a small overpotential of 280 mV at 200 mA·cm–2 in alkaline media. When building an electrolyzer with electrodes of (–)MoO2/MoNi4@Ru/RuO2IIMoO2/ MoNi4@Ru/RuO2 (+), a cell voltage of 1.63 V and 1.75 V is just required to support the current density of 200 mA·cm–2 and 500 mA·cm–2 in alkaline water electrolysis, much lower than that of the electrolyzer of (–)Pt/CIIRuO2(+). This work demonstrates that MoO2/MoNi4@Ru/RuO2 heterogeneous nanosheet arrays are promising candidates for industrial water electrolysis applications, providing a possibility for the exploration of water electrolysis with a large current density.

Novel Pd0.1Cu0.9Co2O4 nano-flake: A promising multifunctional catalyst for the electrochemical water splitting and photo-degradation reactions at ambient temperature

Herein, we report the fabrication of self-assembled Pd0.1Cu0.9Co2O4-nano-flakes via the co-precipitation method. The formation of poly-crystalline cubic spinel phase Pd0.1Cu0.9Co2O4-nano-flake has been identified by powder X-ray diffraction, field emission scanning electron microscopy, and energy dispersive X-ray measurement techniques. The Pd0.1Cu0.9Co2O4 nano-flakes exhibited outstanding activity in the electrochemical water splitting reaction leading to the production of hydrogen and oxygen gas at ambient temperature. Higher current density, lower overpotential, and Tafel slope all are desirable for both HER and OER. Best HER activity (η100 = 628 mV) and capacitive performance in acid was found for Pd-doped electrocatalyst whereas in base the good OER performance (η2 = 434 mV) and capacitive performance was found for CuCo2O4 electrocatalyst. Further, the CPE test demonstrated that Pd0.1Cu0.9Co2O4-nano-flakes are electrochemically stable for 2 h without significant loss in activity. The present catalyst also shows remarkable photocatalytic activity in the degradation of Methylene blue (MB) under visible light at ambient temperature and degrades 100% MB dye in just 1 min. The role of reactive species in the photo-degradation of MB has been established by scavenger tests.

Overlimiting mechanisms of heterogeneous cation- and anion-exchange membranes: A side-by-side comparison

Overlimiting ionic transfer attainable at ion-exchange membranes is a potential way to intensify electromembrane separation processes, such as electrodialysis. The primary mechanisms responsible for overlimiting current are electroconvection, natural convection, and water splitting. For the first time, the present study experimentally investigates all three mechanisms on heterogeneous anion- and cation-exchange membranes, using direct membrane observation and indirect measurement of pH changes in 0.01 M KCl solution. Although the anion- and cation-exchange systems are designed to exhibit the same behavior with different counterions, our results indicate significant differences in the overlimiting ionic transfer. The strong polarization of cation-exchange membranes produced an intensive electroconvective vortex with characteristic velocities in hundreds of μm/s superimposed by an upward electrolyte motion caused by natural convection. No pH changes associated with the water-splitting reaction were observed. The same conditions applied to the anion-exchange membrane resulted in profound pH changes, weaker electroconvection, and natural convection, reaching similar characteristic velocities to the other studied system. Generally, anion-exchange systems were characterized by more significant fluctuations in measured characteristics and were susceptible to fouling by one of the negatively charged markers. The obtained data provide a unified description of phenomena that may occur in the electrodialysis of low-concentrated ionic solutions.

Mn (IV) oxide/Mn (IV) sulfide/poly-2-amino-1-mercaptobenzene for green hydrogen generation

A manganese (IV) oxide (MnO2)–manganese (IV) sulfide (MnS2)/poly-2-amino-1-mercaptobenzene (P2AMB) nanocomposite is prepared through a polymerization reaction (oxidation) and is utilized as a highly photo-electrocatalytic material for green hydrogen generation from sewage water. The manganese (IV) oxide–manganese (IV) sulfide/P2AMB nanocomposite demonstrates remarkable optical properties, characterized by a band gap of 1.81 eV. To promote the water-splitting reaction by the synthesized manganese (IV) oxide–manganese (IV) sulfide/P2AMB nanocomposite photoelectrode, sewage water is utilized as a sacrificial agent to facilitate effectively the generation of hydrogen gas through the evaluation of the current (J ph). At −0.9 V, the J ph and J o values are determined to be −0.33 and −0.2 mA/cm2, respectively. Notably, an optimum J ph value of −0.26 mA/cm2 is observed for incident photons at 340 nm, indicating that light with higher frequency and energy leads to the generation of more electrons from the manganese (IV) oxide–manganese (IV) sulfide/P2AMB nanocomposite and subsequent hydrogen production. Conversely, the lowest J ph value of −0.21 mA/cm2 is obtained at 730 nm, suggesting the influence of infrared waves on the photoelectrode due to the small band gap (1.86 eV) of the materials, as calculated in a previous analysis. This study represents an initial step toward the conversion of wastewater into hydrogen gas, which can serve as a sustainable fuel source for various industrial applications.

Novel Triangulenes: Computational Investigations of Energy Thresholds for Photocatalytic Water Splitting.

Organic materials with Inverted Singlet-Triplet (INVEST) gaps are interesting for their potential use in photocatalytic small molecule transformations such as the entirely solar-driven water splitting reaction. However, only a few INVEST emitters are thermodynamically able to split water requiring a first singlet excited dark state, S1 , above 1.27 or 1.76 eV, and absorption near solar the maximum, 2.57 eV. These requirements and the INVEST character are key for achieving a long-lived photocatalyst for water splitting. The only known INVEST emitters that conform to these criteria are large triangular boron carbon nitrides with unknown synthesis pathways. Using ADC(2), a quantum-mechanical method, we describe three triangulenes. 3 a is a cyano azacyclopenta[cd]phenalene derivative while 3 b and 3 c are cycl[3.3.3]azine derivatives. 3 b has a previously undescribed disulfide bridge. Overall, 3 a fulfills requirements for photocatalytic four-electron reduction of water while the S1 states of 3 b and 3 c are likely slightly low for the two-electron reduction process. By analyzing impacts of ligands, we find that there are guidelines describing how S1 -S5 energies and oscillator strengths, T1 energies, and ΔES1T1 gaps are affected, requiring deep-learning algorithms for which studies will be presented by us in due time. The impact of ground-state geometries, solvation effects, as well as reduced-cost ADC(2) algorithms on our findings are also discussed.