Galvanostatically Deposited PtNi Thin-Films as Electrocatalysts for the Hydrogen Evolution Reaction

The synthesis of hybrid platinum materials is fundamental to enable alkaline water electrolysis for cost-effective H₂ generation. In this work, we have used a galvanostatic method to co-deposit PtNi films onto polycrystalline gold. The surface concentrations of Ni (Γ_Ni) and Pt (Γ_Pt) were calculated from electrochemical measurements; the Γ_Pt/Γ_Ni ratio and electrocatalytic activity of these materials towards hydrogen evolution reaction (HER) in 1 M KOH show a strong dependence on the current density pulse applied during the electrodeposition. Analysis of the Tafel parameters hints that, on these deposits, HER proceeds through a Volmer-Heyrovsky mechanism. The galvanostatically deposited PtNi layers present a high current output per Pt gram, 3199 A g_Pt⁻¹, which is significantly larger compared to other PtNi-based materials obtained by more extended and more complex synthesis methods.     

Introduction of high valent Mo6+ in Prussian blue analog derived Co-layered double hydroxide nanosheets for improved water splitting

Herein, we report a facile method for synthesizing MoCo-layered double hydroxide (LDH) nanosheets employing Prussian blue analog (PBA) as the precursor. The introduction of Mo in Co-LDH modulates the electronic structure, increases the number of active sites and electrochemical surface area to improve the hydrogen evolution, oxygen evolution, and overall water splitting activity. As a result, PBA-derived Mo_0.25Co_0.75-LDH nanosheets demonstrated 10 mA cm^?2 current density at only 220 mV and 115 mV overpotentials for OER and HER, respectively. The overall water splitting was attained at 1.52 V cell voltage for 10 mA cm^?2 current density.     

Circumventing the OCl versus OOH scaling relation in the chlorine evolution reaction: Beyond dimensionally stable anodes

The development of selective electrocatalysts for the chlorine evolution reaction (CER) is majorly restrained by a scaling relation between the OCl and OOH adsorbates, rendering that active CER catalysts are also reasonably active in the competing oxygen evolution reaction (OER). While theory predicts that the OCl versus OOH scaling relation can be circumvented as soon as the elementary reaction steps in the CER comprise the Cl rather than the OCl adsorbate, it was demonstrated recently that PtN₄ sites embedded in a carbon nanotube follow this theoretical prediction. Advanced experimental analyses illustrate that the PtN₄ sites also reveal a different reaction kinetics compared to the industrial benchmark of dimensionally stable anodes (DSA). A reverse Volmer–Heyrovsky mechanism was identified, in which the rate-determining Volmer step for small overpotentials is followed by the kinetically limiting Heyrovsky step for larger overpotentials. Since the PtN₄ sites excel DSA in terms of activity and chlorine selectivity, we suggest the Cl intermediate as well as the reverse Volmer–Heyrovsky mechanism as the design criteria for the development of next-generation electrode materials beyond DSA.     

Hydrogen evolution reaction on Pt and Ru in alkali with volmer-step promotors and electronic structure modulators

Alkaline water electrolysis despite having a variety of choices for anodic oxygen evolution reaction (OER) catalysts out of non-precious metals suffers significantly due to the poor kinetics of cathodic hydrogen evolution reaction (HER) even with the state-of-the-art Pt and equally active Ru. The Volmer-step (water dissociation (WD) coupled proton adsorption) of alkaline HER is mostly the rate-determining step (RDS) and costs most of the work required. In this review, recent developments in improving the HER kinetics of Pt and Ru with Volmer-step promotors and electronic structure modulators have been comprehensively analyzed and critically presented with the challenges and prospects.     

CompassR Yields Highly Organic-Solvent-Tolerant Enzymes through Recombination of Compatible Substitutions

The CompassR (computer-assisted recombination) rule enables, among beneficial substitutions, the identification of those that can be recombined in directed evolution. Herein, a recombination strategy is systematically investigated to minimize experimental efforts and maximize possible improvements. In total, 15 beneficial substitutions from Bacillus subtilis lipase A (BSLA), which improves resistance to the organic cosolvent 1,4-dioxane (DOX), were studied to compare two recombination strategies, the two-gene recombination process (2GenReP) and the in silico guided recombination process (InSiReP), employing CompassR. Remarkably, both strategies yielded a highly DOX-resistant variant, M4 (I12R/Y49R/E65H/N98R/K122E/L124K), with up to 14.6-fold improvement after screening of about 270 clones. M4 has a remarkably enhanced resistance in 60 % (v/v) acetone (6.0-fold), 30 % (v/v) ethanol (2.1-fold), and 60 % (v/v) methanol (2.4-fold) compared with wild-type BSLA. Molecular dynamics simulations revealed that attracting water molecules by charged surface substitutions is the main driver for increasing the DOX resistance of BSLA M4. Both strategies and obtained molecular knowledge can likely be used to improve the properties of other enzymes with a similar α/β-hydrolase fold.     

The Roles of Composition and Mesostructure of Cobalt-Based Spinel Catalysts in Oxygen Evolution Reactions

By using the crystalline precursor decomposition approach and direct co-precipitation the composition and mesostructure of cobalt-based spinels can be controlled. A systematic substitution of cobalt with redox-active iron and redox-inactive magnesium and aluminum in a cobalt spinel with anisotropic particle morphology with a preferred 111 surface termination is presented, resulting in a substitution series including Co₃O₄, MgCo₂O₄, Co₂FeO₄, Co₂AlO₄ and CoFe₂O₄. The role of redox pairs in the spinels is investigated in chemical water oxidation by using ceric ammonium nitrate (CAN test), electrochemical oxygen evolution reaction (OER) and H₂O₂ decomposition. Studying the effect of dominant surface termination, isotropic Co₃O₄ and CoFe₂O₄ catalysts with more or less spherical particles are compared to their anisotropic analogues. For CAN-test and OER, Co³⁺ plays the major role for high activity. In H₂O₂ decomposition, Co²⁺ reveals itself to be of major importance. Redox active cations in the structure enhance the catalytic activity in all reactions. A benefit of a predominant 111 surface termination depends on the cobalt oxidation state in the as-prepared catalysts and the investigated reaction.     

碳自掺杂石墨相氮化碳纳米片的制备及其在可见光照射下的光解水产氢性能

石墨相氮化碳(g?C3N4)由于具有对可见光吸收范围较窄和光生载流子分离效率低等缺陷,其光解水产氢活性较差。我们采用简单的一步热共聚法,以尿素和2,4,6?三氨基嘧啶(TAPD)混合物为前驱物,制备碳自掺杂纳米片(CNNS?x,x mg代表掺入TAPD的质量)。X射线衍射(XRD)、元素分析(EA)和X射线光电子能谱(XPS)等测试结果表明,来自TAPD的嘧啶环成功引入g?C3N4共轭体系中,使所得的CNNS?x具有较窄的带隙,较快的光生载流子迁移速率,从而提高其对可见光的吸收效率和光生载流子的分离效率。得益于此,CNNS?x在可见光照射下表现出较好的光解水产氢活性。特别是CNNS?30具有最佳光解水性能,其产氢速率可达57.6μmol·h-1,是g?C3N4纳米片(CNNS)的4倍。     

Carbon dots/Bi_2WO_6 composite with compensatory photo-electronic effect for overall water photo-splitting at normal pressure

Overall water photo-splitting is a prospective ideal pathway to produce ultra-clean H_2 energy by semiconductors.However,the band structure of many semiconductors cannot satisfy the requirement of H_2 and O_2 production at the same time.Herein,we illustrate that carbon dots(CDs)/Bi_2 WO_6 photocatalyst with compensatory photo-electronic effect has enhanced activity for overall water photo-splitting without any sacrificial agent.In this complex photocatalytic system,the photo-potential provided by CDs makes the CDs/Bi_2 WO6(C-BWO) composite could satisfy the band structure conditions for overall water photo-splitting.The C-BWO composite(3 wt% CDs content) exhibits optimized hydrogen evolution(oxygen evolution) of 0.28 μmol/h(0.12 μmol/h) with an approximate 2:1(H_2:O_2) stoichiometry at normal pressure.We further employed the in-situ transient photovoltage(TPV) technique to study the photoelectron extraction and the interface charge transfer kinetics of this composite catalyst.     

Transition metal-based electrocatalysts for overall water splitting

Electrochemical overall water splitting is attracting a broad focus as a promising strategy for converting the electrical output of renewable resources into chemical fuels, specifically oxygen and hydrogen. However, the urgent challenge in water electrolysis is to search for low-cost, high-efficiency catalysts based on earth-abundant elements as an alternative to the high-cost but effective noble metal-based catalysts. The transition metal-based catalysts are more appealing than the noble metal catalysts because of its low cost, high performance and long stability. Some recent advances for the development in overall water splitting are reviewed in terms of transition metal-based oxides, carbides, phosphides, sulfides, and hybrids of their mixtures as hybrid bifunctional electrocatalysts. Concentrating on different catalytic mechanisms, recent advances in their structural design, controllable synthesis, mechanistic insight, and performance-enhancing strategies are proposed. The challenges and prospects for the future development of transition metal-based bifunctional electrocatalysts are also addressed.     

Surface oxidized iron-nickel nanorods anchoring on graphene architectures for oxygen evolution reaction

Surface oxidized iron-nickel nanorods coupling with reduced graphene architectures (FeNi-O-rGA) are successfully constructed via hydrothermal, freeze-drying, and thermal activation approaches. The hierarchical structure can provide lots of pathways for fast ion diffusion and charge transfer, and expose abundant catalytic sites. Meanwhile, the activity of FeNi-O-rGA is boosted by the optimized metal-oxygen bond strength in FeNi₃ alloys. Partial oxidized FeNi nanorods are strongly coupled with rGA by the formation of metal-O-C bonds, which can impede the aggregation of FeNi₃ alloys and increase the utilization of active sites. The special structure and partially oxidized FeNi nanorods for FeNi-O-rGA can result in excellent OER activity and catalytic stability. Only 215 mV of overpotential is required to drive the current density of 10 mA/cm² as well as the Tafel slope of 50.9 mV/dec in 1 mol/L KOH. The change of surface chemistry of FeNi-O-rGA is confirmed by XPS after the OER test, which indicates the highly catalytic stability of FeNi-O-rGA due to the formation of intermediate metal oxyhydroxide.