Reaction In Acid Medium Research Articles

Electrocatalysts for the Oxygen Evolution Reaction in Acidic Media.

The well-established proton exchange membrane (PEM)-based water electrolysis, which operates under acidic conditions, possesses many advantages compared to alkaline water electrolysis, such as compact design, higher voltage efficiency, and higher gas purity. However, PEM-based water electrolysis is hampered by the low efficiency, instability, and high cost of anodic electrocatalysts for the oxygen evolution reaction (OER). In this review, the recently reported acidic OER electrocatalysts are comprehensively summarized, classified, and discussed. The related fundamental studies on OER mechanisms and the relationship between activity and stability are particularly highlighted in order to provide an atomistic-level understanding for OER catalysis. A stability test protocol is suggested to evaluate the intrinsic activity degradation. Some current challenges and unresolved questions, such as the usage of carbon-based materials and the differences between the electrocatalyst performances in acidic electrolytes and PEM-based electrolyzers are also discussed. Finally, suggestions for the most promising electrocatalysts and a perspective for future research are outlined. This review presents a fresh impetus and guideline to the rational design and synthesis of high-performance acidic OER electrocatalysts for PEM-based water electrolysis.

Insight into the stability mechanism of nickel and manganese antimonate catalytic films during the oxygen evolution reaction in acidic media

Electrochemical water splitting in acidic media is a promising approach for generating hydrogen (H2) gas as a green fuel. In this regard, catalyst design for the oxygen evolution reaction (OER) is more demanding due to the slow transfer kinetics of involved four electrons and high corrosion and degradation of the electrode. Besides, a sustainable OER catalyst should be noble metal-free and have long-term durability under positive potentials in acidic solutions. The current study suggests a nickel-manganese-antimony electrocatalyst synthesized via a facile thermal decomposition method for OER in 0.5 M sulfuric acid. The proposed electrode can generate a current density up to 400 mA cm−2 and withstand 168 h electrolysis under 10 mA cm−2 with an initial overpotential of 598 mV. This stability is largely superior to most of the reported noble metal-free OER catalysts, and the activity has been improved >70 mV compared to the other reported Sb-based electrodes. The 1 week electrochemical stability in acidic media was thoroughly studied by XPS and XRD to analyze the chemical composition and morphology of the electrode before and after the OER, respectively.

Carbon black supported PtCu nanoparticles derived from mix‐phased Cu precursor for high‐performanced oxygen reduction reaction in acid medium

AbstractAlloying high‐cost Pt with transition metals has been considered as an effective route to synthesize the electrocatalysts with low Pt loading and excellent activity towards oxygen reduction reaction (ORR) under acid solution. The galvanic replacement method, as featured with efficiency and simplicity, is widely reported to produce Pt‐based bimetallic alloys and thereby declare the significance of reductive transition metal precursor on the enhancement of ORR performance. Herein, mix‐phased Cu−Cu2O precursor was applied to prepare carbon black supported highly dispersed PtCu alloy nanoparticles (PtCu/C). The proper Cu−Cu2O ratios can exactly facilitate the generation of small sized PtCu alloy nanoparticles with regulated bimetallic content. Meanwhile, the Cu2O phase is revealed to benefit the electron transfer from Pt to Cu and thus improve the intrinsic activity of Pt active sites. And the metallic Cu can favor the promotion of electrochemical active surface area. Consequently, the as‐prepared PtCu/C behaves impressive ORR activity with half‐wave potential of 0.88 V (vs. RHE) and mass activity of 0.49 A cm−2 mgPt−1 at 0.8 V, which is 9.8 times of commercial Pt/C catalysts. Our work will offer helpful advices for the development and regulation of novel Pt‐based alloy materials towards diverse electrocatalysis.

Development of a highly stable and active non-precious anode electrocatalyst for oxygen evolution reaction in acidic medium based on nickel and cobalt-containing antimony oxide

The electrocatalysts anodes using base metals on titanium substrate by sol–gel method were synthesized as an alternative due to the scarcity of noble metals, such as iridium and ruthenium. For this purpose, the cobalt antimonate and nickel–cobalt antimonate stable electrocatalysts to carry out the oxygen evolution reaction (OER) were developed. LSV showed that the cobalt antimonate electrocatalyst has an intrinsic potential of 1.615 V vs. RHE. For the cobalt antimonate electrocatalyst, the potential corresponding to the current density of 10 mA.cm−2 is 1.791 V vs. RHE. The stability of all synthesized anodes at a current density of 10 mA.cm−2 was at least 200 h (more than 8 days) while the CoSb2Ox electrocatalyst displayed a superior lifetime for at least 650 h (more than 27 days) at a current density of 100 mA.cm−2. According to the EIS data at the potential of 1.791 V vs. RHE, the nickel–cobalt antimonate had the lowest charge transfer resistance (Rct) of 4 Ω.cm2. The combination of the above results confirms the capability of the proposed anode as a substitute for precious ones.

Facile green synthesis of Ag/carbon nanotubes composite for efficient water splitting applications

Taking advantage of the multi-walled carbon nanotubes in enhancing electrical conductivity and gas generation, metallic silver/carbon nanotube composite (Ag@CNT) was prepared by a facile approach using green tea extract without calcination or high-temperature treatment to enhance both hydrogen (HER) and oxygen (OER) evolution reactions in acidic media. Various physicochemical methods have been utilized to characterize the synthesized Ag@CNT composite, including thermal analysis (TA), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and powder X-ray diffraction (XRD). The fabricated GC/Ag@CNT modified electrodes have been tested for hydrogen evolution in various supporting electrolytes such as H2SO4, NaOH, and Na2SO4. The electrochemical performance of the Ag@CNT electrocatalyst toward hydrogen production in 0.5 M H2SO4 was compared to both pristine CNT and Ag. Results confirmed that current densities of 10 mA cm−2 at overpotentials of − 0.35, − 0.38, and − 0.46 V (vs. RHE) have been obtained for GC/Ag@CNT, GC/Ag, and GC/CNT, respectively, reflecting the enhanced electrocatalysis for the designed composite. Furthermore, marked decrease in the estimated Tafel slopes for the fabricated GC/Ag@CNT (98 mV dec−1) compared to GC/Ag modified electrode (157 mV dec−1) is consistent with facile electrode kinetics. Electrochemical impedance spectroscopy was also employed to determine hydrogen evolution's charge-transfer resistance (RCt) at the three different surfaces. Finally, hydrogen atom adsorption on silver, CNT, and Ag@CNT surfaces was probed via density-functional theory (DFT) whereas energy profile of hydrogen molecules formation was investigated using the Dmol3 numerical model.

Stabilizing Ni atoms on PtNi crystals by constructing PtNix-(CeO2)y heterostructures for improving durability of oxygen reduction reaction in acidic media

The oxygen reduction reaction (ORR) activity of PtNi alloys is easily decreased on account of the Ni leaching under the harsh acidic environment. Therefore, we prepared a PtNi1.5-(CeO2)0.8/C electrocatalyst with abundant PtNi1.5-(CeO2)0.8 interfaces by a wet-chemical synthesis strategy. Electrochemical tests revealed that PtNi1.5-(CeO2)0.8/C exhibits excellent ORR performance with mass activity (MA) of 551.1 mA mgPt−1 and specific activity (SA) of 1.3 mA cmPt−2 @ 0.9 V vs. RHE, respectively, which are better than commercial JM Pt/C (MA of 152.9 mA mgPt−1 and SA of 0.2 mA cmPt−2@ 0.9 V vs. RHE). More interestingly, it displays remarkable durability with 9.0% of its initial MA loss after 10,000 CV cycles, outperforming JM Pt/C (a 15.1% loss) and PtNi1.5/C counterparts (a 35.5% loss). The density functional theory (DFT) calculations explained that the electronic interaction at interfaces leads to a lower d-band center (εd) and weaker oxygen adsorption energy E(ads)(O) in Pt atoms of PtNi1.5-(CeO2)0.8 than that in Pt NPs, which is favorable for the desorption of O* and promotes the ORR process. Furthermore, the diffusion energy barrier E(FS-IS) of Ni atoms in PtNi1.5-(CeO2)0.8 from subsurface to surface is higher than that in PtNi1.5 counterparts, indicating the Ni leaching can be decelerated.

Retrofitting of carbon-supported bimetallic Ni-based catalysts by phosphorization for hydrogen evolution reaction in acidic media

Commercial bimetallic Ni–Mo and Ni–Re electrocatalysts supported on advanced conductive carbon are high-performing materials for H2 evolution reaction in alkaline medium, but they cannot be applied in acidic medium due to the rapid dissolution of metals. In this work, we solve this issue by introducing a convenient phosphorization protocol to convert these commercial metallic electrocatalysts into the respective phosphides, rendering them stable under acidic conditions, and thus providing a pathway to electrocatalysts for water reduction in acidic electrolyte. The novel materials demonstrate high performance, as reflected by the measured low overpotentials, shallow Tafel slopes, fast kinetics, as well as excellent stability and durability. This work opens the possibility to expand the applicability of commercial supported metallic catalysts and electrocatalysts through retrofitting via phosphorization.

Development of Unsupported Ru and Ni Based Oxides with Enhanced Performance for the Oxygen Evolution Reaction in Acidic Media

Development of Unsupported Ru and Ni Based Oxides with Enhanced Performance for the Oxygen Evolution Reaction in Acidic Media

Charge-enriched RuO2 nanoparticles decorating TiO2 with Ti defects to promote oxygen evolution reaction in acidic media

RuO2 supported metal-deficient TiO2 substrate presents superior electrocatalytic activity for OER in acidic media, which is attributed to the introduction of Ti defects modulated the local electronic structures of Ru sites and TiO2 substrate.

High activity and excellent durability of oxygen-vacancy-rich ruthenium manganese oxide solid-solution nanowires for the oxygen evolution reaction in acidic media

Oxygen vacancy-rich solid-solution RuxMn1−xO2 nanowires have been reported to be efficient catalysts for acidic oxygen evolution reaction. They only need an overpotential of 200 mV to drive 10 mA cm−2 and show no obvious activity drop for >600 h.

Ruthenium doping in the MoS2/AB heterostructure for the hydrogen evolution reaction in acidic media.

Electrocatalyst design is an important approach to prompt the commercialization of water electrolysis technologies. In this work, a ruthenium doped MoS2/AB heterostructure is synthesized as an electrocatalyst for the hydrogen evolution reaction (HER) through hydrothermal and annealing processes. The physical-chemical characterization studies show that the MoS2/AB heterostructure and the incorporation of Ru effectively induce a phase transition from 2H to 1T-MoS2. The as-prepared Ru-MoS2/AB exhibits an excellent HER performance with a very low overpotential of 13 mV at 10 mA cm-2 and a Tafel slope of 31 mV dec-1 in 0.5 M H2SO4, remarkably higher than those of Pt/C (overpotential of 28 mV at 10 mA cm-2, 41 mV dec-1). Density functional theory calculations suggest that the H absorption on Ru bonding to S exhibits a rather low binding energy (-0.22 eV), indicating the optimum active sites of Ru near S for HER. Significantly, the Ru-MoS2/AB also demonstrates high stability under long-term discharge and elevated temperature conditions. These results suggest that the as-prepared Ru-MoS2/AB can be a promising alternative to Pt/C for water electrolysis, due to its high HER activity, easy synthesis, and good stability.

Pd-based bimetallic electrocatalysts for hydrogen oxidation reaction in acidic medium

Pd-based bimetallic electrocatalysts for hydrogen oxidation reaction in acidic medium

Modification of TiO2 nanotubes by graphene–strontium and cobalt molybdate perovskite for efficient hydrogen evolution reaction in acidic medium

Herein, we demonstrate that modification of TiO2 nanotubes with graphene–strontium and cobalt molybdate perovskite can turn them into active electrocatalysts for hydrogen evolution reaction (HER). For this purpose, a simple method of hydrothermal synthesis of perovskites was developed directly on the TiO2 nanotubes substrate. Moreover, the obtained hybrids were also decorated with graphene oxide (GO) during one-step hydrothermal synthesis. The obtained materials were characterized by scanning electron microscopy with energy dispersive X-ray analysis, Raman spectroscopy, and X-ray diffraction analysis. Catalytic properties were verified by electrochemical methods (linear voltammetry, chronopotentiometry). The obtained hybrids were characterized by much better catalytic properties towards hydrogen evolution reaction compared to TiO2 and slightly worse than platinum. The optimized hybrid catalyst (decorated by GO) can drive a cathodic current density of 10 mA cm−2 at an overpotential of 121 mV for HER with a small Tafel slope of 90 mV dec−1 in 0.2 M H2SO4.

Iridium-titanium oxides for efficient oxygen evolution reaction in acidic media

Active and highly stable oxygen evolution reaction (OER) electrocatalyst for PEM-based water electrolysis are currently in high demand. Herein, we report a rutile iridium-titanium oxide solid solution (IrTiOx) through a facile one-step annealing of a Ti-based metal-organic framework precursor. The composite exhibits excellent OER activity and stability in acidic media, with a low overpotential of 296 mV at 10 mA cm−2 while the OER activity was retained during a 100-h galvanostatic stability test at a constant current of 10 mA cm−2 in 0.5 M H2SO4, outperforming the state-of-the-art IrO2-based electrocatalysts. We further demonstrate the structure evolution of iridium-titanium oxide during OER operations. In contrast to the initial uniform distribution of Ir and Ti over the entire architecture, after OER stability test, a hollow morphology is formed, in which the particle surface is covered with an IrOx-rich layer and entire particle becomes hollow. We ascribe the structure evolution to the Ir/Ti leaching and redeposition during the OER operations. We propose that the structure evolution of iridium-titanium oxide during the electrochemical process is responsible for the high OER activity and stability of IrTiOx.

Surface Modulation of Fe3O4 Confined in Porous Molybdenum‐Based Nanoplatform for Enhanced Hydrogen Production

The integration of different precursor components to form single nanostructures via one‐step synthesis process is mostly restricted by the compatibility and complexity of components. Herein, a highly uniform, spherical, hollowed, and hierarchical iron oxide‐wrapped Mo–polydopamine is synthesized using a one‐pot liquid‐phase reaction at room temperature. Mo2C is doped with Fe3O4 to harness the rich electrons in Fe dopants for effective lowering of the unoccupied d‐orbitals in Mo. The surface conductivity of the as‐prepared nanostructures is enhanced by decorating them with gold nanoparticles utilizing strong interaction of Au and amine. The nanocomposites are converted into carbidic hollowed structures via an annealing process without any distortion in morphology. The well‐organized structure and nanosize of the particles provide efficient catalytic performance for hydrogen evolution reaction in acidic media. MoFe–C@Au exhibits a very positive onset potential of 2 mV, low Tafel slope of 50.1 mV dec−1, and remarkable long‐term stability.

Pd/Hemin-rGO as a bifunctional electrocatalyst for enhanced ethanol oxidation reaction in alkaline media and hydrogen evolution reaction in acidic media

H2 generation needs a cost-effective, robust, stable, long-durable, and super-active electrocatalyst. This study reveals a rapid and facile method for fabricating Pd NPs on Hemin-rGO as novel support. The obtained electrocatalyst was characterized by UV–Vis, XPS, FESEM, EDS, HRTEM, and AFM. The electrochemical measurements reveal the superb effect of Hemin-rGO for enhancing the catalytic activity of Pd as bifunctional electrocatalysts for hybrid water electrolysis (hydrogen evolution reaction (HER) and ethanol electrooxidation reaction (EOR)). Pd/Hemin-rGO displays a low peak potential (−210 V) with remarkable current density (1.95 A mg−1 Pd) in 0.1 M EtOH and 0.1 M NaOH. The ratio of jf/jb of Pd/Hemin-rGO compared with Pd electrocatalyst reveals this novel support's ani-poisoning effect. Besides, it shows the Tafel slope of 26 mV dec−1 and overpotentials of 47 and 131 mV were obtained at 10 and 100 mA cm−2 in acidic media toward HER. Exploring and designing new electrocatalysts may be enhanced by this research, which can use Hemin as a novel support for noble metals such as Pt, Pd, Rh, Au, and Ru for diverse energy-related applications.

Morphology-Controlled Synthesis of V1.11S2 for Electrocatalytic Hydrogen Evolution Reaction in Acid Media.

High-performance low-cost catalysts are in high demand for the hydrogen evolution reaction (HER). In the present study, we reported that V1.11S2 materials with flower-like, flake-like, and porous morphologies were successfully synthesized by hydrothermal synthesis and subsequent calcination. The effects of morphology on hydrogen evolution performance were studied. Results show that flower-like V1.11S2 exhibits the best electrocatalytic activity for HER, achieving both high activity and preferable stability in 0.5 M H2SO4 solution. The main reason can be ascribed to the abundance of catalytically active sites and low charge transfer resistance.

A highly stable Tungsten-Doped TiO2-Supported platinum electrocatalyst for oxygen reduction reaction in acidic media

The carbon-supported platinum electrocatalyst’s severe carbon corrosion issue in acidic media limits the widespread application of proton exchange membrane fuel cells (PEMFCs). Therefore, exploring novel noncarbon supports with improved corrosion resistance is needed to resolve this problem. This research presented tungsten-modified titanium dioxide (W-doped TiO2) support for the Pt catalyst toward the oxygen reduction reaction (ORR). W-doped TiO2 showed a higher surface area and more Ti3+ defect sites and oxygen vacancies than the undoped TiO2 support, which enhanced strong metal support interaction for the deposited Pt catalyst. Furthermore, the high ORR activity of the Pt/W-doped TiO2 catalyst was demonstrated using a high electrochemical surface area of 44.1 m2/gPt and mass activity value of 41.22 A/gPt for electrochemical performance in 0.1 M HClO4. Moreover, the rotating ring-disk electrode measurement of the Pt/W-doped TiO2 catalyst under acidic conditions showed a four-electron pathway with an ultrasmall peroxide yield of 0.42 %. Particularly, the durability test showed that the Pt/W-doped TiO2 had a remarkable stability compared to commercial catalysts. Therefore, this study provides a promising pathway to improve the stability of Pt-based catalysts for PEMFCs.

Highly durable core(Nb4N5)–shell(NbOx)-structured non-precious metal catalyst for oxygen reduction reaction in acidic media

In this study, we demonstrate an easy and eco-friendly synthesis method of Nb-based electrocatalysts using the combination of pulsed laser ablation in liquid and ammonia nitriding at various temperatures and times. Our electrocatalyst samples had a nanoparticle size with a core–shell structure, where the niobium nitride core was surrounded by a thin layer of niobium oxide shell. The nitriding conditions for the samples successfully modified the core structure to become more electrically conductive. The Nb4N5 @NbOx/C_5 h, the sample heat-treated at 900 °C for 5 h, exhibited a moderate onset potential and catalytic activity. More importantly, the oxygen reduction reaction performance of the Nb4N5 @NbOx/C_5h sample did not degrade over 10,000 potential cycles. Based on the above results, we suggest that the nitride core and the thin layer of the oxide shell might be responsible for oxygen reduction by facilitating electron transport and providing oxygen adsorption sites.

Electrocatalytic Behavior of an Amide Functionalized Mn(II) Coordination Polymer on ORR, OER and HER.

The new 3D coordination polymer (CP) [Mn(L)(HCOO)]n (Mn-CP) [L = 4-(pyridin-4-ylcarbamoyl)benzoate] was synthesised via a hydrothermal reaction using the pyridyl amide functionalized benzoic acid HL. It was characterized by elemental, FT-IR spectroscopy, single-crystal and powder X-ray diffraction (PXRD) analyses. Its structural features were disclosed by single-crystal X-ray diffraction analysis, which revealed a 3D structure with the monoclinic space group P21/c. Its performance as an electrocatalyst for oxygen reduction (ORR), oxygen evolution (OER), and hydrogen evolution (HER) reactions was tested in both acidic (0.5 M H2SO4) and alkaline (0.1 M KOH) media. A distinct reduction peak was observed at 0.53 V vs. RHE in 0.1 M KOH, which corresponds to the oxygen reduction, thus clearly demonstrating the material's activity for the ORR. Tafel analysis revealed a Tafel slope of 101 mV dec-1 with mixed kinetics of 2e- and 4e- pathways indicated by the Koutecky-Levich analysis. Conversely, the ORR peak was not present in 0.5 M H2SO4 indicating no activity of Mn-CP for this reaction in acidic media. In addition, Mn-CP demonstrated a noteworthy activity toward OER and HER in acidic media, in contrast to what was observed in 0.1 M KOH.