High Reaction Activity Research Articles

Ru0.1Mn0.9Ox Electrocatalyst for Durable Oxygen Evolution in Acid Seawater

AbstractCurrently, direct electrolysis of seawater for green hydrogen production is primarily focused on neutral and alkaline systems. However, the precipitation of calcium and magnesium ions restricts the advancement of this technology. An acidic system can effectively address this issue. Given that Ru/Ir‐based catalysts with high oxygen evolution reaction (OER) activity also exhibit high chlorine evolution reaction (CER) activity, acid seawater splitting requires anodes with higher selectivity and stability compared to the other two systems. In this study, we propose a non‐precious Ru0.1Mn0.9Ox as the active anode for direct acid seawater electrolysis, which exhibits a high OER selectivity and remarkable stability for more than 1200 hours. Different from the Cl−‐free system, *Cl occupied on Ru sites could shift the OER active center to Mn on Ru0.1Mn0.9Ox, which prevents the lattice oxygen consumed on Ru and hinders the metal site dissolution. As the CER‐insensitive catalytic center, Mn activated by the introduction of Ru can adsorb a substantial amount of *OH, creating an OER‐favored local environment that inhibits CER. We introduce Cl−‐assisted transfer of OER active sites to CER‐insensitive Mn as a fundamental strategy for achieving highly selective and durable oxygen evolution in acidic seawater.

Construction of δ-FeOOH/NiMn2S4 heterointerface for efficient alkaline oxygen evolution reaction

Alkaline water electrolysis driven by sustainable energy is a viable approach for large-scale green hydrogen production. The development of non-precious metal-based electrocatalysts that combine high activity and stability for the alkaline oxygen evolution reaction (OER) is of great importance. In this work, we design and construct a δ-FeOOH/NiMn2S4/NF heterointerface using a solvothermal/calcination process followed by a facile successive ionic layer adsorption reaction (SILAR) treatment. Experimental tests indicate that the formation of the heterogeneous interface between the δ-FeOOH and the NiMn2S4 creates a good electron transport channel for an efficient electrocatalytic process and improves the charge transfer kinetics. As a result, the prepared δ-FeOOH/NiMn2S4/NF exhibits a low overpotential of 210 mV at 10 mA cm−2 and a low Tafel slope value of 46.6 mV dec−1, and satisfactory stability with a 92.9 % retention after 72 h of OER operation at around 100 mA cm−2. In situ Raman and in-situ attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) tests show that the introduction of δ-FeOOH inhibits the oxidation of Ni2+ to Ni3+ and stabilizes the Ni-S bond to prevent its auto-oxidation, leads to an increase in the electrocatalytic OER activity.

Activation of ammonium oxalate on dandelion-derived nitrogen-doped carbon for electrocatalytic oxygen reduction reaction

Development of electrocatalysts with high catalytic activity for the oxygen reduction reaction (ORR) plays an important role in sustainable energy technology. Herein, a carbon-based electrocatalyst was prepared by pyrolyzing the dandelion straw, accompanied with the activation of ammonium oxalate (AO) for the first time. Based on the physical characterization, the DAO-1100 exhibits a well-developed pore structure, rich morphologies, high surface area, high graphitization degree, as well as high total content of pyridinic nitrogen and graphitic nitrogen. Therefore, DAO-1100 shows excellent electrocatalytic activity for ORR at the onset potential of 0.991 V, half-wave potential of 0.883 V and limiting diffusion current of 5.30 mA·cm−2 approximately, in comparison to those of the Pt/C catalyst. DAO-1100 catalyzes the ORR through a 4 e- pathway like Pt/C catalyst. In addition, it also possesses the better operational durability and catalytic selectivity than those of Pt/C catalyst. Therefore, ammonium oxalate, serving as a low-cost, efficient activator, can efficiently promote the transformation of abundant dandelion straw to metal-free biochar catalysts.

Supramolecular pre‐organisation rhodium and iridium metal complexes within M12L24 self‐assembled nanospheres for the confined synthesis Rh/Ir alloyed nanoparticles

Controlling the size and composition of metal nanoparticles is of considerable interest, as these are essential to their catalytic properties. We report the controlled synthesis Rh nanoparticles by preorganisation of metal complexes inside Pt12L24 nanospheres based on complementary hydrogen bonds before the reduction step that leads to nanoparticle formation. The encapsulated RhI complexes (Rh‐s @ G‐sphere) led to reasonable size control (2.8 ± 0.9 nm). We also report the formation of Rh‐Ir alloyed nanoparticles with varying Rh/Ir compositions. These heterometallic particles were evaluated in the hydrogenation of cinnamaldehyde (7) as a probe reaction. Besides a high activity in this probe reaction, the Rh particles also catalyzed the conversion of the solvent (CH3CN). The formed basic amine leads to follow‐up reactions of the product and compatibility issues with the hosting nanosphere. The solvent hydrogenation was effectively suppressed by using the Rh:Ir alloyed nanoparticles, provided that they contain >66% Ir. The Rh:Ir alloyed nanoparticles displayed high catalytic activity, reaching optimal selectivity and activity at an 8:16 ‐ Rh:Ir ratio. The combined catalytic results illustrate that pre‐organisation of the metal complexes in the nanosphere before the reduction with hydrogen effectively facilitates the formation of Rh:Ir alloyed nanoparticles.

Iron Doping of 2D Nickel-Based Metal-Organic Frameworks Enhances the Lattice Heterogeneous Interface Coupling Effect for Improved Electrocatalytic Oxygen Evolution.

The coupling of lattice and heterostructure interfaces represents an effective strategy for disrupting the so-called scalar relationship and accelerating reactions involving multiple intermediates. In view of this, a lattice-heterostructure interfacial catalyst consisting of a crystalline Fe/Ni bimetallic MOF and amorphous Fe-MOF was designed in this paper for high-performance alkaline oxygen evolution reaction electrocatalysis. The strongly coupled lattice-heterostructure interface induces a unique synergistic effect that promotes electron transfer of the catalyst. The resulting catalyst exhibits exceptionally high catalytic activity for the oxygen evolution reaction in alkaline media, the Ni9Fe1-BDC-1@Fe-MOF coated on a glassy carbon electrode has an overpotential of 257 mV at a current density of 10 mA cm-2. Furthermore, this catalyst demonstrates a high electrochemical stability. These research results highlight the superiority of lattice-heterostructure interfaces in the development of advanced catalysts.

Electrocatalytic mechanism for overall water splitting to produce sustainable hydrogen by 2D Janus MoSH monolayer

In the present work, we investigates the potential of two dimensional (2D) Janus MoSH monolayer as an electrocatalyst for overall water splitting using first-principles calculations. Our results shows that 2D Janus MoSH monolayer exhibits excellent structural stability and electronic properties, which are essential for efficient electrocatalysis. We find that the charge transfer mechanism between Mo and S atoms plays a crucial role in the electrocatalytic activity of 2D Janus MoSH monolayer. Due to the asymmetric structure of MoSH monolayer, it has intrinsic electric field with dipole moment of 0.24 D. Moreover, we demonstrate that 2D Janus MoSH monolayer exhibits high catalytic activity for both hydrogen evolution reaction (HER) with overpotential 0.04 V and oxygen evolution reaction (OER) with overpotential 0.11 V, making it a promising candidate for overall water splitting. Our findings have significant implications for the design and optimization of 2D monolayered materials for renewable energy production. By providing insights into the underlying mechanisms of HER and OER on 2D Janus MoSH monolayer, our study paves the way for the development of efficient and sustainable electrocatalysts for water splitting. We hope that current work will be helpful in understanding the electrocatalytic mechanism of 2D Janus MoSH monolayer and its potential applications in renewable energy production.

Ru0.1Mn0.9Ox Electrocatalyst for Durable Oxygen Evolution in Acid Seawater.

Currently, direct electrolysis of seawater for green hydrogen production is primarily focused on neutral and alkaline systems. However, the precipitation of calcium and magnesium ions restricts the advancement of this technology. An acidic system can effectively address this issue. Given that Ru/Ir-based catalysts with high oxygen evolution reaction (OER) activity also exhibit high chlorine evolution reaction (CER) activity, acid seawater splitting requires anodes with higher selectivity and stability compared to the other two systems. In this study, we propose a non-precious Ru0.1Mn0.9Ox as the active anode for direct acid seawater electrolysis, which exhibits a high OER selectivity and remarkable stability for more than 1200 hours. Different from the Cl--free system, *Cl occupied on Ru sites could shift the OER active center to Mn on Ru0.1Mn0.9Ox, which prevents the lattice oxygen consumed on Ru and hinders the metal site dissolution. As the CER-insensitive catalytic center, Mn activated by the introduction of Ru can adsorb a substantial amount of *OH, creating an OER-favored local environment that inhibits CER. We introduce Cl--assisted transfer of OER active sites to CER-insensitive Mn as a fundamental strategy for achieving highly selective and durable oxygen evolution in acidic seawater.

MoZn-based high entropy alloy catalysts enabled dual activation and stabilization in alkaline oxygen evolution.

It remains a grand challenge to develop electrocatalysts with simultaneously high activity, long durability, and low cost for the oxygen evolution reaction (OER), originating from two competing reaction pathways and often trade-off performances. The adsorbed evolution mechanism (AEM) suffers from sluggish kinetics due to a linear scaling relationship, while the lattice oxygen mechanism (LOM) causes unstable structures due to lattice oxygen escape. We propose a MoZnFeCoNi high-entropy alloy (HEA) incorporating AEM-promoter Mo and LOM-active Zn to achieve dual activation and stabilization for efficient and durable OER. Density functional theory and chemical probe experiments confirmed dual-mechanism activation, with representative Co-Co†-Mo sites facilitating AEM and Zn-O†-Ni sites enhancing LOM, resulting in an ultralow OER overpotential (η10 = 221 mV). The multielement interaction, high-entropy structure, and carbon network notably enhance structural stability for durable catalysis (>1500 hours at 100 mA cm-2). Our work offers a viable approach to concurrently enhance OER activity and stability by designing HEA catalysts to enable dual-mechanism synergy.

Construction of CeO2/Co(OH)2/FeS@NF nanosheet arrays for high-performance electrocatalytic oxygen evolution/urea oxidation, and overall water/urea splitting reactions

To develop non-noble electrocatalysts with high activity and stability for oxygen evolution reaction (OER)/urea oxidation reaction (UOR) is crucial to boost the efficiency of overall water/urea splitting reaction (OWS/OUS) for H2 production. Herein, we synthesized novel CeO2/Co(OH)2/FeS nanosheet arrays on nickel foam (CeO2/Co(OH)2/FeS@NF) through a simple two-step hydrothermal and following solvothermal routine. In this special structure, the ultra-thin 2D nanosheet morphology can adequately offer large contact area and thus abundant of active sites, facilitating significantly the mass transfer. Furthermore, the incorporation of FeS into CeO2/Co(OH)2 will not only modify the electron structure but also provide a number of phase interfaces, which can improve the inherent electron conductivity and promote the electron transport. More importantly, the rich oxygen vacancies (Ov) sites can vary the coordination of metal centers, modulating both the charge distribution and M−O bonding strength. As results, the CeO2/Co(OH)2/FeS@NF shows superior low overpotentials of 178 mV/1.30 V at 10 mA cm−2 to OER/UOR. The activity keeps its low value of 232 mV/1.375 V even when the current density was increased to as high as 300 mA cm−2. More importantly, the electrode of CeO2/Co(OH)2/FeS@NF//CeO2/Co(OH)2/FeS@NF just requires a low cell voltage of 1.41 V to realize OUS at a current density of 10 mA cm−2. Specifically, we also realized solar-driven H2 production. Plenty of H2 bubbles were continuously generated with a high speed of 600 L h−1 m−2 on the working electrode surface once the solar panel was placed under the natural sunlight.

Cuboidal molybdenum sulfur cluster as a platform to construct novel catalyst for propane dehydrogenation

Growing demand of short chain olefins such as propylene for plastic production drives the development of high performing catalysts for propane dehydrogenation (PDH). Here, a confinement strategy originating from metal-sulfur clusters was employed to fabricate defective MoPtSx phase via anchoring by coordinatively unsaturated Al sites present on alumina, followed by reduction under H2 flow at high temperature. This catalyst with a low Pt content exhibits great ability for C–H activation with high intrinsic activity and facile propylene desorption in PDH reaction. More importantly, this catalyst shows excellent stability during long-term tests with both stable conversion and selectivity. Through combined X-ray absorption spectroscopy, electron microscopy and electron paramagnetic resonance measurements it could be affirmed that the isolated and electron-enriched Pt sites as well as their proximity to adjacent sulfur vacancies is vital for the first and second C–H bond activation, and suppressing of C–C cleavage which otherwise lead to coking.

Cavity-Based Discovery of New Fatty Acid Photodecarboxylases.

Light-dependent fatty acid photodecarboxylases (FAPs) hold significant potential for biotechnology, due to their capability to produce alka(e)nes directly from the corresponding (un)saturated natural fatty acids requiring light as the only reagent. This study expands the family of FAPs through cavity-based enzyme discovery methods. Thirty enzyme candidates with potential photodecarboxylation activity were identified by matching the cavities of four related template structures against the Protein Data Bank's flavoproteins, a library of proteins identified via the Foldseek Search Server, and homology models of sequences resulting from BLAST. Subsequent docking experiments narrowed this library to ten promising enzymes, which were expressed and assessed in vitro, identifying four photodecarboxylases. Out of these enzymes, the GMC oxidoreductase from Coccomyxa sp. Obi (CoFAP) was characterized in detail, which revealed high activity in the decarboxylation reactions of palmitic acid and octanoic acid and a broad pH tolerance (pH 6.5-9.5).

Internal Electron-Donation Allocation Design for Intrinsic Solubilization of Lithium Nitrate in Ester Electrolyte for Stable Lithium Metal Batteries.

Lithium metal batteries (LMBs) have become a hot topic in the research of next-generation advanced battery technology due to their high specific energy. However, the high reaction activity between lithium metal and electrolyte is considered one of the key bottlenecks limiting large-scale applications of LMBs. As a classic electrolyte additive, LiNO3 significantly improves the stability of lithium metal in ether-based electrolytes. However, its solubility in carbonate-based electrolytes widely used in lithium-ion batteries is extremely low, and its protective effect on lithium metal is limited, which has become a key obstacle to the commercial application of lithium metal batteries. Here, we enhanced the local negative charge density of carbonyl oxygen atoms in carbonate molecules by introducing electron donors, making it easier for them to coordinate with Li+, thereby weakening the interaction between Li+ and NO3-, and significantly increasing the solubility of LiNO3 in ester electrolytes. The modified ester solvent promotes the derivatization and decomposition of salt anions, leading to the formation of a dense SEI layer rich in LiF and LiNxOy. This significantly improves the stability of lithium metal in ester-based electrolytes. The assembled Li||Li symmetric battery shows excellent cycling performance of over 4000 hours.

Heterointerfacial engineering of N,P-doped carbon nanosheets supported Co/Co2P nanoparticles for boosting oxygen reduction and oxygen evolution reactions towards rechargeable Zn-air battery

Transition metal phosphides (TMPs) with high electrocatalytic activity for the oxygen evolution reaction (OER) are reckoned as a substitution of precious group metals catalysts in rechargeable Zn-air battery. In this work, Co/Co2P heterojunction nanoparticles supported N,P-doped carbon nanosheets (Co/Co2P@NPCNS) were designed and prepared via a facile one-step molten salt-assisted pyrolysis process. Density function theory calculations reveal that the heterogeneous interactions of Co/Co2P effectively enhance the bifunctional electrocatalytic activity for oxygen reduction reaction (ORR) and OER. The synergistic interaction between the Co/Co2P heterojunction nanoparticles with highly exposed active sites and excellent catalytic activity and the two-dimensional doped carbon nanosheets with high conductivity contributes to Co/Co2P@NPCNS exhibiting preeminent bifunctional ORR/OER activity and stability with a high half-wave potential for ORR (0.87 V), a low overpotential for OER (302 mV at 10 mA cm−2) and a low potential gap (0.66 V). The homemade rechargeable Zn-air battery performs high peak power density (187 mW cm−2) and exceptional endurance. This heterogeneous interface tactic of integrating TMPs with heteroatom-doped carbon materials may shed light on the research and development of non-precious metal electrocatalysts.

Aerobic Thiols Oxidative Coupling to Disulfides over Robust CoOx Nanoclusters Confined within Hierarchical Silicalite-1 Zeolite.

Disulfide is an important organic reagent and synthetic intermediate that is widely used in organic synthesis, polymers, and other fields, but its synthesis still suffers from many environmental pollution and economic problems. Here, we present an environmentally friendly and efficient base-free aerobic oxidative thiol coupling catalyzed by heterogeneous CoOx nanoclusters entrapped in hierarchical silicalite-1 zeolite, synthesized by combining silane pore expansion and metal coordination methods under hydrothermal conditions. It is confirmed that open hierarchical channels favor mass diffusion, and the chemical valence of Co species in CoOx/h-S-1-H is +2, which is different from that of Co3O4 particles in CoOx/h-S-1-I. CoOx nanoclusters, are strongly fixed in the channels of silicalite-1 zeolite via Co-O-Si bonds, which is of great importance for the high catalytic activity in both symmetrical and unsymmetrical oxidative thiol coupling reactions. After recycling experiments four times, the CoOx/h-S-1-H used has almost the same chemical state and the same distribution of Co(II) species as the fresh catalysts. Based on DFT calculations and inhibition experiments, the oxidative coupling of thiols undergoes a free radical mechanism in which Co(III) causes RS-H cleavage into RS· and H· species. Subsequently, two RS· radicals are coupled to disulfides, while H· radicals react with the O species to form H2O molecules. This work not only provides guidance on catalyst design and parameter optimization for oxidative thiol coupling but also advances the understanding of the aerobic oxidation mechanism.

Pd-Co Supported on Anodized Aluminium for VOCs Abatement: Reaction Mechanism, Kinetics and Applicability as Monolithic Catalyst

It has been found out that Pd-Co-based catalyst, supported on anodized aluminum, possesses very high activity in combustion reactions of C1–C6 alkanes and toluene. The catalyst characterization has been made by N2-pysisorption, XRD, SEM, XPS, FTIR, TEM, and EPR methods. In view of the great interest, methane combustion was investigated in detail. It is ascertained that the complete oxidation of methane proceeds by dissociative adsorption on PdO and formation of hydroxyl and methyl groups, the former being highly reactive, and it undergoes further reaction to oxygen-containing intermediates, whereupon HCHO is one of them. The presence of Co2+ cations promotes greatly oxygen adsorption. The dissociative adsorption is favored on neighboring Co2+ cations, leading to the formation of bridging peroxides. Further, the oxygen dissociates on the nearest Pd2+ cations. According to the results from the experimental data, instrumental methods, and the observed kinetics and DFT model calculations, it can be concluded that the reaction pathway over Pd+Co/anodic alumina support (AAS) catalyst proceeds most probably through Mars–van Krevelen. The obtained data on the kinetics were used for simulation of the methane combustion in a full-scale adiabatic reactor.

Hollow Nanobox‐Shaped Cu2‐xS@ZnxCd1‐xS Heterojunction by Light Multireflection with Z‐Scheme Mechanism for Enhanced Photocatalytic Hydrogen Production

AbstractAchieving efficient spatial photoinduced charge separation and light utilization for improving the high photocatalytic activity is still a major obstacle. Here, a Cu2‐xS@ZnxCd1‐xS (Cu2‐xS@ZnCdS) heterojunction is reported featuring a distinctive core–shell hollow nanobox structure. The Cu2‐xS@ZnxCd1‐xS exhibits high photocatalytic activity in hydrogen evolution reaction (HER) at the rate of 8175 µmol∙g−1∙h−1 under visible light irradiation, outperforming pristine ZnCdS nanoparticles and Cu2‐xS hollow nanoboxes. The remarkable activity and outstanding stability of Cu2‐x@ZnCdS are attributed to the development of robust interfacial electric fields, and improved light multireflection absorption efficiency as well as the Z‐scheme mechanism. The electron paramagnetic resonance (EPR) and in situ X‐ray photoelectron spectroscopy (XPS) measurements gave the direct evidence of the formation of the Z‐scheme, which maintained the high redox potentials of each ZnCdS and Cu2‐xS. This study gives the guideline for the design of heterojunction with the Z‐scheme mechanism, leading to the high photocatalytic performance and remarkable stability.

Boosting OER activity of Fe-N Moieties via Ni induced d-Orbital Tailoring for durable rechargeable Zn-Air batteries

Fe-N-C-based catalysts are considered the most promising Pt candidates due to their high oxygen reduction reaction (ORR) activity and low cost, whereas their oxygen evolution reaction (OER) performance is extremely poor due to the sluggish O-O coupling process, which hampers the practical application of rechargeable zinc-air batteries. Here, we in situ infiltrate Ni and Fe ions into metal triazolidine (MET)-derived N-doped porous carbon via a microporous confinement-pyrolysis strategy to enhance the OER activity of the Fe-N sites. The introduction of Ni induced the electronic delocalization of Fe atoms at the Fe-N center, which lowered the adsorption energy barriers for the decisive velocity step (O*→OOH*), thus accelerating the O-O bond coupling and OER kinetics. In addition, the preferential formation of NiOOH at high OER potentials ensures the catalytic stability of zinc-air batteries by trapping Fe ions escaping from carbon corrosion to form FeOOH. The optimized catalyst (FeNi-NC) has an overpotential of only 351 mV at a current density of 50 mA cm−2 under alkaline conditions. More importantly, the assembled ZABs can be stably charged and discharged for more than 500 h at 10 mA cm−2, demonstrating excellent battery charging and discharging stability. This work shows the great potential of strong electronic interactions between polymetals to improve Fe-N-C catalysts.

Self-Reconstruction Induced Electronic Metal-Support Interaction for Modulated Cu+ Sites on TiO2 Nanofibers in Electrocatalytic Nitrate Conversion.

The Cu+ active sites have gained great attention in electrochemical nitrate reduction, offering a highly promising method for nitrate removal from water bodies. However, challenges arise from the instability of the Cu+ state and microscopic structure over prolonged operation, limiting the selectivity and durability of Cu+-based electrodes. Herein, a self-reconstructed Cu2O/TiO2 nanofibers (Cu2O/TiO2 NFs) catalyst, demonstrating exceptional stability over 50 cycles (12 h per cycle), a high NO3 --N removal rate of 90.2%, and N2 selectivity of 98.7% is reported. The in situ electrochemical reduction contributes to the self-reconstruction of Cu2O/TiO2 nanofibers with stabilized Cu+ sites via the electronic metal-support interaction between TiO2 substrates, as evidenced by in situ characterizations and theoretical simulations. Additionally, density functional theory (DFT) calculations also indicate that the well-retained Cu+ sites enhance catalytic capability by inhibiting the hydrogen evolution reaction and optimizing the binding energy of *NO on the Cu2O/TiO2 NFs heterostructure surface. This work proposes an effective strategy for preserving low-valence-state Cu-based catalysts with high intrinsic activity for nitrate reduction reaction (NO3RR), thereby advancing the prospects for sustainable nitrate remediation technologies.

Flexible PET/Carbon/NiFe‐LDH Electrode for Oxygen Evolution Reaction in Water‐Splitting

AbstractThe development of low‐cost, readily scalable catalytic systems for green hydrogen production is crucial for diverse research and industrial applications. This work demonstrates the facile coupling of carbon/NiFe‐layered double hydroxide (LDH) onto flexible polyethylene terephthalate (PET) substrates deposited by blade coating and spray coating techniques. These low‐temperature solution processes enable high‐throughput electrode fabrication. The resulting carbon electrode exhibits sheet resistance of 25 Ω sq−1, comparable to other state‐of‐the‐art works, and displays excellent adhesion to the substrate and catalyst layer, thereby ensuring system stability. Remarkably, the developed electrode exhibits high catalytic activity for the oxygen evolution reaction (OER), achieving an overpotential of 215.9 and 267.4 mV at 10 mA cm−2 in rigid and flexible substrates respectively, and maintaining its performance even at 10 mA cm−2 for 24 h. This work highlights the potential of this methodology for producing readily transportable, flexible electrocatalytic systems with exceptional performance and minimal surface treatment of the substrate. Additionally, the use of low‐cost, readily recyclable PET plastic aligns with the principles of circular economy, promoting the integration of this platform into both research and industrial environments.

Electrochemical and electrocatalytic properties of hemihexaphyrazine and its trinuclear cobalt complex

The electrochemical and electrocatalytic properties of hemihexaphyrazine and its trinuclear cobalt complex were studied by cyclic voltammetry. The possibility of detecting cationic and anionic forms of compounds in the process of polarization of electrodes in the region of potentials 0.5 ÷ -1.5 V has been established. It is shown that the synthesized cobalt complex has a sufficiently high catalytic activity in the oxygen reduction reaction in an alkaline solution.