Oxygen Evolution Activity Research Articles

Reinforcement of Electrocatalytic Oxygen Evolution Activity Enabled by Constructing Silver-Incorporated NiCo-PBA@NiFe-LDH Hierarchical Nanoboxes.

Complicated oxygen evolution reaction (OER) poses the bottleneck in improving the efficiency of hydrogen production through water electrolysis. Herein, an integrated strategy to modulate the electronic structure of NiFe layered double hydroxide (NiFe-LDH) is reported by constructing Ag-incorporated NiCo-PBA@NiFe-LDH heterojunction with a hierarchical hollow structure. This "double heterojunction" facilitates local charge polarization at the interface, thereby promoting electron transfer and reducing the adsorption energy of intermediates, ultimately enhancing the intrinsic activity of the catalyst. It is noteworthy that an exchange bias field is observed between NiCo-PBA and NiFe-LDH, which will be conducive to regulating the electron spin states of metals and facilitating the production of triplet oxygen. Additionally, the unique hierarchical nanoboxes provide a large specific surface area that ensures adequate exposure to adsorption sites and active sites. Profiting from the synergistic advantages, the overpotential is as low as 190mV at a current density of 10mAcm-2, with a low Tafel slope of 21mVdec-1. Moreover, density functional theory (DFT) calculation further substantiated that the incorporation of Ag in the heterojunction can effectively reduce the adsorption energy of reactant intermediates and enhance the conductivity.

In situ Construction of Multistage Core-Shell Nanostructure as Bifunctional Catalyst for Ultrastable Zinc-Air Batteries.

Many efforts have been devoted to obtaining excellent cathode catalysts for Zinc air batteries (ZABs), but the inevitable use of binder will damage the catalytic activity and weaken long-term stability, inefficient mass transfer of oxygen is also chargable for the limited activity. Herein, in situ grown hydrogen substituted graphdiyne (HGDY) on carbon paper has been prepared and used as cathode catalyst layer in ZABs. Multiple catalytic sites are firmly combined and end with the boosted bifunctional catalytic activity of oxygen reduction and oxygen evolution. Moreover, the specific surface area, sufficient active sites, multilevel pore nanostructure and robust conductivity are fully exposed to establish efficient catalytic interface and skeleton. Cu/Co nanoparticles are uniformly distributed and warped by HGDY network, which can stably exist during the catalytic process. As a result, a current density of 18.75mAcm-2 and a Tafel slope of 61.06mVdec-1 for oxygen reduction and a ultralong operation for more than 2300h in aqueous ZAB have been achieved, which is beyond many reported bifunctional catalysts in ZAB system.

Enhanced Oxygen Evolution Activity and Stability of RuO2(110) Surface by Ti Doping

Introduction Developing highly active and durable electrocatalysts for the oxygen evolution reaction (OER) is essential for efficient hydrogen production through polymer electrolyte membrane water electrolysis (PEMWE). Although RuO2 exhibits the highest OER activity among pure transition metal oxide catalysts, its low durability hampers its practical application as an OER catalyst for PEMWE. Recent studies have shown that the incorporation of dissimilar metal elements, such as Ni, Mn, and Cu, effectively enhances the OER activity and stability of RuO2 in acidic electrolytes (1-3). In this study, we focus on Ti, a corrosion-resistant element in the PEMWE environment, and investigate the effects of doping amounts on the OER activity and stability of a RuO2(110) single crystal model catalyst surface. Experimental Non-doped rutile-type TiO2(110) single crystals were used as sample substrates. Ru and Ti, with a total thickness of 40 nm, were deposited onto the substrate at 400 ℃ under 0.5 Pa-O2 partial pressure using the arc-plasma deposition (APD) method. Subsequently, the sample was post-annealed at 400℃ for 1 hour in air using a tube furnace. Hereafter, the samples are denoted as RuO2-Tix (x represents the atomic percentage of doped Ti).Oxygen evolution activity was measured by linear sweep voltammetry (LSV) at a scan rate of 20 mV s-1 in N2-purged 0.1 M HClO4 at room temperature. Chronopotentiometry (CP) was conducted at 1 mA cm-2 for 120 min to evaluate the durability. The electrochemical impedance spectroscopy was conducted at 1.6 V vs. reversible hydrogen electrode (RHE) to measure the solution resistance. All the LSV and CP data were iR-corrected using the Rs values. Out-of-plane X-ray diffraction (XRD) analysis was carried out to evaluate the crystal structure. The dissolution amounts of Ru into the electrolyte after CP were evaluated by inductively coupled plasma mass spectrometry (ICP-MS). Results and Discussions Fig. 1(a) presents the out-of-plane XRD patterns of Ti-doped and non-doped RuO2(110) samples. The results indicate that (110)-oriented Ti-doped and non-doped RuO2 thin films were successfully obtained on TiO2 substrates. However, the peak position of RuO2(110) gradually shifts to the lower angle side, and the peak becomes less distinct with increasing Ti-doping amounts, suggesting that doped Ti is dissolved in the RuO2 crystal lattice and the crystallinity decreases with increasing doping amounts. Initial LSV curves for OER are shown in Fig. 1(b). The current density of RuO2-Ti4, 5, and 7 samples significantly increases at higher potential regions above 1.6 V vs. RHE, while RuO2-Ti2 and 10 exhibit decreased activity. The CP curves presented in (c) demonstrate that Ti doping, especially at 5 and 7 at.%, effectively suppresses the overpotential increase during CP. The dissolution amounts of Ru after 120 min of CP are summarized in (d). The dissolution amounts tend to decrease with increasing Ti-doping amounts. These results clearly show that an appropriate amount of Ti-doping effectively enhances both the OER activity and electrochemical stability of the RuO2(110) surface.AcknowledgmentsThis study was partly supported by JSPS KAKENHI Grant Number 21H01661, 22K19078 and Toyota Mobility Foundation Hydrogen Initiative. References Z. Y. Wu, F. Y. Chen, B. Li, S. W. Yu, Y. Z. Finfrock, D. M. Meira, Q. Q. Yan, P. Zhu, M. X. Chen, T. W. Song, Z. Yin, H. W. Liang, S. Zhang, G. Wang and H. Wang, Nat. Mater., 22, 100 (2023). S. Chen, H. Huang, P. Jiang, K. Yang, J. Diao, S. Gong, S. Liu, M. Huang, H. Wang and Q. Chen, ACS Catal., 10, 1152 (2020). J. Su, R. Ge, K. Jiang, Y. Dong, F. Hao, Z. Tian, G. Chen and L. Chen, Adv Mater, 30, 1801351 (2018). Figure 1

Investigation of Transition Metal Oxides & Phosphates for Zn-Ion/Zn-Air Batteries

Being a champion in a portable electronics world, lithium-ion batteries (LIBs) are irreplaceable, but the scarcity of Li, high cost, and the inclusion of non-aqueous electrolytes make them relatively perilous and inefficient for grid-scale energy storage. Recently, the blooming aqueous Zn-ion batteries (ZIBs) have emerged as one of the pioneer candidates featuring the inherently safe nature of metallic Zn anode and its unique properties.[1] Vanadium-based compounds show fast ion diffusion and excellent reversible capacity because of their rich valence state of vanadium, facile distortion of V-O polyhedrons, and tuneable composition, which offers an excellent treasure house. Moreover, the different oxidation states of vanadium allow a higher degree of structural change and greater functional flexibility while incorporating multivalent cations into vanadium-based compounds. [2] The present work focuses on one V-based oxide cathode. The cathode, ZnV2O4, synthesized by a simple solid-state route, showed a reversible capacity of around 200 mAh/g at a current density of 500 mA/g. Ex-situ XAS suggested that there is a drastic change in V and Zn local environment, confirming that there is a structural transformation taking place. Further, we have pursued ex-situ TEM where segregation of the conversion product phases was seen, confirmed by the small crystalline domains present at the nanoscale regime. A detailed analysis will be discussed to verify that a phase transformation is happening and is getting amorphized in subsequent cycles using ex-situ TEM and XAS.Also, metal-air batteries are widely discussed and studied because of their high energy density. In this pursuit, highly efficient bifunctional electrocatalysts, non-noble such as Co metal-based phosphates/oxides, have been studied vividly.[3,4] Herein, we present a thorough study of three-dimensional ZnCo2(PO4)2 (ZCP), which showed excellent bifunctional activity compared to the benchmark catalysts, denoting the presence of many catalytically active Co sites in ZCP. The presence of asymmetric edge-sharing CoO5/CoO6 polyhedra enhances the net catalytic activity.[5] ZCP exhibited robust oxygen reduction and evolution (ORR and OER) activity with the onset of 0.87 and 1.50 V vs. RHE for ORR and OER, respectively. The ORR saturated current density for ZCP was 6.38 mA/cm2, close to the 20% Pt/C catalyst benchmark. It also showed an OER exchange current density of 16.7 mA/cm2, closer to RuO2 ( j= 17.6 mA/cm2). This bifunctional electrocatalytic activity will be elaborated using analytical tools and DFT, along with the demonstration of Zn-air batteries. A detailed structural characterization using synchrotron refinement, TEM analysis, magnetic studies, and electrocatalysis performance will be discussed. Reference s : [1] M. Song et al., Adv. Funct. Mater. 2018, 28, 1802564.[2] Yao. Zhang et al., Chem. Front. 2021, 5 744-762.[3] J. L. Jung et al., Energy Environ. Sci. 2016, 9176-183.[4] W. Liu et al., Acc. Chem. Res . 2018,51,1858.[5] A. Baby et al., Chem. Comm. 2020, 56, 8400-8403.

Ru Perovskites with Enhanced Activity and Durability for the OER in Acid Media

Iridium- and Ruthenium based catalysts are the only feasible ones for the oxygen evolution reaction (OER) in acidic media. The high price and scarcity of Ir is a major hurdle to realize electrolysis in the GW-scale. Ru-based catalysts can be suitable candidates to replace Ir, since they are more active for the OER than Ir. However, Ru catalysts lack sufficient stability during the OER. This is because, Ru tends to form soluble upper oxides e.g. RuO4 at high voltages (> 1.4 V). Previous studies reveal that Na- or K-doping can increase Ru’s durability during the OER.1,2 However, recent studies demonstrate that Ru’s activity and stability depends on the structure and composition of the Ru-based catalyst.3 In this work, we report a series of Ru double perovskites, namely R2NiRuO6 (R = Pr, Nd, Tb, Dy, Y, Ho and Er)4 with low ruthenium content and high OER activity in acidic electrolyte. The oxides have been synthesized by wet-chemistry and thoroughly characterized by XRD (Rietveld refinement), TEM and XPS.The OER was studied in the rotating ring disk (RDE) configuration in 0.1 M HClO4. Due to the absence of Sr or alkali metals in their structure, in addition to displaying high initial OER activity, the perovskites are stable during OER cycles between 1.1 and 1.7 V, with Dy2NiRuO6 being stable at least during 500 consecutive cycles (see Figures 1a and 1b).Characterization results reveal that Ru-O distances in the perovskites follow the order Dy<Er<Y<Ho<Tb<Nd<Pr. As shown in Figure 1c, the OER activity, i.e., the potential recorded at 10 mA·cm-2, follows the same trend. Also, the durability of the catalysts follows the same trend.The smaller Ru-O distance indicates a higher oxidation state of Ru atoms in Dy2NiRuO6. In addition, the gives symmetry and order to the structure. perovskite, making it more stableXPS and TEM-EDS post-mortem studies of Dy2NiRuO6 reveal a loss of Ni after 500 OER cycles and the presence of Ru3+ cations, being the main cause of the loss of OER activity.The R2NiRuO6 double perovskites reported in this work are the first example of highly active and stable Ru-based perovskites for the OER in acidic electrolyte that can opens the way for the replacement of Ir from state of the art PEMWEs.(1) Retuerto, M.; Pascual, L.; Calle-Vallejo, F.; Ferrer, P.; Gianolio, D.; Pereira, A. G.; García, Á.; Torrero, J.; Fernández-Díaz, M. T.; Bencok, P.; Peña, M. A.; Fierro, J. L. G.; Rojas, S. Na-Doped Ruthenium Perovskite Electrocatalysts with Improved Oxygen Evolution Activity and Durability in Acidic Media. Nat. Commun. 2019, 10 (1), 2041. https://doi.org/10.1038/s41467-019-09791-w.(2) Rodríguez-García, I.; Galyamin, D.; Pascual, L.; Ferrer, P.; Peña, M. A.; Grinter, D.; Held, G.; Abdel Salam, M.; Mokhtar, M.; Narasimharao, K.; Retuerto, M.; Rojas, S. Enhanced Stability of SrRuO3 Mixed Oxide via Monovalent Doping in Sr1-XKxRuO3 for the Oxygen Evolution Reaction. J. Power Sources 2022, 521, 230950. https://doi.org/10.1016/j.jpowsour.2021.230950.(3) Paoli, E. A.; Masini, F.; Frydendal, R.; Deiana, D.; Malacrida, P.; Hansen, T. W.; Chorkendorff, I.; Stephens, I. E. L. Fine-Tuning the Activity of Oxygen Evolution Catalysts: The Effect of Oxidation Pre-Treatment on Size-Selected Ru Nanoparticles. Catal. Today 2016, 262, 57–64. https://doi.org/10.1016/j.cattod.2015.10.005.(4) Kayser, P.; Alonso, J. A.; Muñoz, A.; Fernández-Díaz, M. T. Structural and Magnetic Characterization of the Double Perovskites R2NiRuO6 (R = Pr-Er): A Neutron Diffraction Study. Acta Mater. 2017, 126, 114–123. https://doi.org/10.1016/j.actamat.2016.12.024. Figure 1

Perovskite-Type Oxynitride Nanofibers Performing Photocatalytic Oxygen and Hydrogen Generation

(111)-layered perovskites such as Ba5Ta4O15 or Ba5Nb4O15 are known for their promising activity in hydrogen evolution and overall water splitting.[1] Their activity can be further enhanced by the preparation of Ba5Ta4O15-Ba3Ta5O15-BaTa2O6 composites.[2,3] However these materials can only absorb UV-light, which prevents them to be used in solar-light induced photocatalysis. Therefore, the preparation of visible-light absorbing photocatalysts is very important for future application in solar-light induced hydrogen evolution and overall water splitting.Perovskite-type oxynitrides AB(O,N)3 are one group of materials which can absorb visible light, i.e. BaNbO2N with an absorption edge up to 740 nm.[4-7] These perovskite-type oxynitrides can be quite easily prepared by ammonolysis of (111)-layered perovskites, due to their structural similarity of 6-fold coordinated B cations, corner-shared BO6 octahedra, and the 12-fold oxygen coordinated A cations in both crystal structures.[8] However, this conversion often results in micrometer-sized particles due to the high temperatures used in the ammonolysis process, thus resulting in small surface areas.[6,7] Therefore, the nanostructuring of such perovskite-type oxynitrides can be of interest, due to the higher surface area and shorter diffusion pathways of the minority charge carriers. One possibility to nanostructure photocatalysts and enhance the photocatalytic activity is the electrospinning of nanofibers. Hildebrandt et al. and Bloesser et al. reported the preparation of highly crystalline Ba5Nb4O15, Ba5Ta4O15, and Ba5Nb2Ta2O15 (111)-layered perovskite nanofibers and the tailoring of the nanofiber diameter of Ba5Ta4O15 and Ba5Ta4O15-Ba3Ta5O15 nanofibers by electrospinning.[9-11]Herein, we present a novel approach for the preparation of nanostructured complex perovskite oxynitrides.[12] Ba5Nb4O15 (111)-layered perovskite nanofibers with tailored nanofiber diameters were electrospun and converted via ammonolysis. Most importantly, the nanofiber morphology was maintained during ammonolysis, and the nanofiber diameter could be adjusted as well. A thorough characterization, including Rietveld refinement, revealed the formation of a novel BaNbO2N-Ba2NbO3N perovskite oxynitride composite. UV-vis measurements further supported the results of a BaNbO2N-Ba2NbO3N composite formation and revealed a reduction of the band edge by more than 2 eV from 3.9 eV for Ba5Nb4O15 to 1.7 eV for the converted nanofiber composites. A diameter-dependent hydrogen and oxygen evolution activity of the BaNbO2N-Ba2NbO3N composite nanofibers after deposition of Pt or CoNbO4, respectively, with an optimum nanofiber diameter will be presented.[1] Y. Miseki et al. Energy Environ. Sci. 2019, 2, 306 [2] J. Soldat, et al. Chem. Sci. 2014, 5, 3746[3] A. Hofmann et al. J. Phys. Energy 2021, 3, 014002[4] T. Hisatomi et al., Energy Environ. Sci., 2013, 6, 3595[5] J. Seo et al., J. Mater. C hem. A, 2019, 7, 493[6] M. Hojamberdiev et al., J. Mater. Chem. A, 2016, 4, 12807[7] T. Yamada et al., J. Phys. Chem. C, 2018, 122, 8037[8] S. Ramaraj et al. J. Energy Chem. 2022, 68, 529[9] N. C. Hildebrandt et al., Small, 2015, 11, 2051 [10] A. Bloesser et al., J. Mater. Chem. A, 2018, 6, 1971[11] A. Bloesser, R. Marschall, ACS Appl. Energy Mater. 2018, 1, 2520[12] A. Hofmann et al., Adv. Mater. Interfaces, 2021, 8, 2100813

Advanced and Scalable Polyol-Mediated Synthesis Route for Highly Active Ni Metal Sulfides (M = Fe, Mn, Cr, Mo) As Efficient Electrocatalysts for Sea/Saline Water Oxidation

Recent studies have made significant progress in addressing oxygen evolution (OER), a bottleneck reaction in water electrolysis, by utilizing innovative electrode materials and catalysts to enable low-grade and saline water splitting, thus offering promising prospects for advancing sustainable hydrogen production systems.1 This study applied a modified polyol-mediated strategy2 to describe an advanced procedure for synthesizing NiMSx where M = (Fe, Mn, Cr, Mo). Several physical and chemical characterization tools are applied to investigate the obtained saline/seawater oxidation electrocatalysts, including XRD, SEM, TEM, and electrochemical characterization. The outcomes of these characterizations were displayed as graphs. The catalysts reveal nanoclusters morphologies. The figure below depicts the preliminary findings, illustrating the electrochemical performance and the physical characterizations. Figure 1 (a) and (b) represent the polarisation curves of the oxygen evolution activity of the synthesized MNiSx electrocatalysts on Carbon cloth and Ni foam working electrodes, respectively, in a three-electrode configuration with Pt wire serving as the counter and Hg/HgO serving as the reference electrode in 1M KOH plus natural seawater from the Galway Bay Ireland. The catalysts obtained a high current exchange density of above and close to the 200 mAcm-2. Figure 1(c) displays the images of the catalyst-coated working electrodes prepared via dip coating, both Ni foam and carbon cloth, while Figures 1(d) and 1(e) reveal the nanostructure-based clusters of the produced materials with the scanning and transmission electron microscopy, respectively. In addition, we are evaluating the efficacy of this high-performance anode electrocatalyst in a single cell with a working electrode area of 3 cm2 for the oxygen evolution reaction (OER) and Pt/C as a cathode for hydrogen evolution reaction (HER). Our research project aims to develop highly efficient Oxygen Evolution Reaction (OER) catalysts.We will employ various ex-situ and in-situ characterization techniques, including, Impedance spectroscopy, chronopotentiometry/chronoamperometry, Powder X-ray diffraction (XRD), Raman spectroscopy, and FTIR spectroscopy. Impedance spectroscopy determines the system's impedance as a function of frequency and offers insights into electrochemical behavior, such as resistance, capacitance, and charge transfer resistance. Chronopotentiometry/chronoamperometry will be applied to check the long-term stabilities of catalysts. X-ray diffraction (XRD) will examine the crystal structure of the stimuli in real-time during OER. X-ray photoelectron spectroscopy (XPS) will be applied to analyze the materials' surface chemistry and elemental composition by measuring the energies of emitted photoelectrons from X-ray irradiation. In-situ Raman spectroscopy will enable us to study changes in the catalysts' electronic structure and coordination environment during the reaction providing valuable insights into the underlying mechanism of OER. FTIR spectroscopy will reveal information about the response intermediates and mechanisms during OER. We can obtain a detailed understanding of the reaction pathway by monitoring the changes in the vibrational spectra of the reactants and products. Finally, post-mortem analysis of the catalysts will be performed after electrochemical testing to assess their degradation. Above all will help us optimize the catalysts' design for long-term stability and high-performance OER. Acknowledgments The authors acknowledge the ANEMEL Project funded by the Horizon Europe (European Innovation Council) Grant agreement 101071111. References Tong, W.; Forster, M.; Dionigi, F.; Dresp, S.; Sadeghi Erami, R.; Strasser, P.; Cowan, A. J.; Farràs, P., Electrolysis of low-grade and saline surface water. Nature Energy 2020, 5 (5), 367-377. Zhang, H.; Hyun, B.-R.; Wise, F. W.; Robinson, R. D., A generic method for rational scalable synthesis of monodisperse metal sulfide nanocrystals. Nano letters 2012, 12 (11), 5856-5860. Figure 1

Ce and S co-doped NiFe based alloy nanocomposite prepared by one-step electrodeposition method for oxygen evolution reaction

It's still a challenge to design reasonably efficient catalyst using non-noble metal for the oxygen evolution reaction (OER). In this paper, we use a simple one-step electrodeposition method to load Ce and S co-doped NiFe amorphous alloys onto Cu(OH)2 nanorod arrays. The excellent oxygen electrocatalytic performance of the catalyst NiFeCeS/Cu(OH)2/CuF is attributed to the electronic environments of the active sites of Ni and Fe regulated by heteroatomic sulfur and cerium, which promote the transfer of the oxygen precipitation intermediates to the higher valence states. Meanwhile, the highly conductive substrate accelerates the electron transfer efficiency of the catalyst material, and the loose nanostructure increases the specific surface area, exposing more active sites. NiFeCeS/Cu(OH)2/CuF shows outsanding electrocatalytic activity for oxygen evolution with a low overpotential of 227 mV at a current density of 10 mA cm−2 in alkaline medium. Moreover, the nanocomposite catalyst also exhibits rapid reaction kinetics and long-term stability and durability. In this work, an efficient oxygen precipitation catalyst is reported, which indicates that non-precious metal-based electrocatalysts have great potential for application in water electrolysis and provides a basis for the rational design and synthesis of nanorod array catalysts with unique structures.

Oxidative Depolymerisation of Kraft Lignin: From Fabrication of Multi‐Metal‐Modified Electrodes For Vanillin Electrogeneration via Pulse Electrolysis To High‐Throughput Screening of Multi‐Metal Composites

AbstractThe production of green hydrogen may be greatly aided by the use of an alternative anode reaction replacing oxygen evolution to increase energy efficiency and concomitantly generate value‐added products. Lignin, a major component of plant matter, is accumulated in large amounts in the pulp and paper industry as waste. It has excellent potential as a source of aromatic compounds and can be transformed into the much more valuable aroma chemical vanillin by electrochemical depolymerisation. We used a flow‐through model electrolyser to evaluate electrocatalyst‐modified Ni foam electrodes prepared by a scalable spray‐polymer preparation method for oxidative lignin depolymerisation. We demonstrate how pulsing, i. e. continuously cycling between a lower and a higher applied current, increases the amount of formed vanillin while improving the energy efficiency. Further, we present a scanning droplet cell‐assisted high‐throughput screening approach to discover suitable catalyst materials for lignin electrooxidation considering that a suitable electrocatalyst should exhibit high activity for lignin depolymerization and simultaneously a low activity for vanillin oxidation and oxygen evolution. Combining electrosynthesis and electrocatalysis can aid in developing new customised materials for electrochemical processes of potential industrial interest.

Interfacial P–O covalent bonds regulated electronic configuration in black phosphorus for improving oxygen evolution activity

Black phosphorus (P(black)) shows impressive physicochemical features for electrocatalysis including adjustable bandgap and high charge carrier mobility. However, the existence of solitary electron pairs in exfoliated P(black) nanosheets (EP(black)) leads to rapid surface degradation, resulting in unfavorable durability. Herein, a P–O bridge was created in the heterostructure EP(black)/vanadium-doped cobalt hydroxide with oxygen vacancy (EP(black)/V–CoO2-xH2) to stabilize and expedite oxygen evolution reaction (OER) activity. By bonding the solitary electron pairs of EP(black) and oxygen species (OH*) of V–CoO2-xH2, the distinctive P–O bridge resulted in important ligand effects that improved not merely the stability of EP(black) but effectively regulated the electron configuration of V–CoO2-xH2. DFT simulations revealed that directional interfacial electron migration from V–CoO2-xH2 to EP(black) facilitated the formation of pivotal OER intermediates and hence boosted OER activities. This study proposes a novel strategy to enhance the electrochemical properties of EP(black), which could be extended to a wide range of high-performance electrocatalyst systems.

Simultaneous Morphology and Band Structure Manipulation of BiOBr by Te Doping for Enhanced Photocatalytic Oxygen Evolution.

The photocatalytic oxygen evolution of bismuth oxybromide (BiOBr) is greatly hindered by its low visible-light response and high electron-hole recombination. Nonmetal doping can effectively alleviate these issues, leading to improvement in photocatalytic performance. Herein, Bi2Te3 was introduced as both the Te doping source and the morphology-control template to improve the photocatalytic performance of BiOBr. Appropriate amounts of Te are critical to maintain the ultrathin plate-like structure of BiOBr, whereas excessive Te results in the formation of a flower-like architecture. Oxygen evolution activity disclosed that a plate-like structure is essential for realizing higher performance owing to sufficient light utilization and efficient charge separation. An optimal oxygen evolution rate of 368.0 μmol h-1 g-1 was achieved for the Te-doped sample, which is 2.3-fold as that of the undoped BiOBr (158.9 μmol h-1 g-1). Theoretical calculations demonstrated that Te doping can induce impurity levels above the valence band of BiOBr, which slightly narrowed the band gap and strengthened the light absorption in the range of 400-800 nm. More importantly, Te dopants could act as shallow traps for confining the excited electrons, thus prolonging the carrier lifetime. This work provides a novel strategy to prepare highly efficient photocatalysts by simultaneously realizing morphology manipulation and nonmetal doping.

Plasma-induced vacancy defects of Ru-doped CoFe layered double hydroxide for superior oxygen evolution activity

CoFe layered double hydroxide (CoFe LDH) can serve as a cost-effective and active electrocatalyst for oxygen evolution reaction (OER). Unfortunately, it still faces the challenges of low electrical conductivity, stability and limited active sites to achieve the threshold current density with low overpotential. In this study, the strategy of Ru doped together with air plasma treatment was proposed to improve the OER performances of CoFe LDH. The doping of Ru and air plasma process could induce electronic interaction and the oxygen defects to regulate the electronic structure. Significantly, the air plasma treated Ru doped CoFe LDH (P-Ru-CoFe LDH) catalyst achieved superior catalytic properties to the CoFe LDH and RuO2 benchmarks, which was demonstrated by a relatively smaller overpotential of 275 mV at 10 mA cm−2 and a lower Tafel slope of 107 mV dec−1 for OER. In addition, it also maintained an excellent stability in long-term chronoamperometry test. In general, P-Ru-CoFe LDH catalyst could boost the OER performance through intrinsic electronic structure adjustment with Ru doped and air plasma process. These findings provide an effective pathway to design/develop OER electrocatalysts with high performances by internal electron coupling effects.

Sputtered Stainless Steel on Silicon Photoanode for Stable Seawater Splitting in Photoelectrochemical Flow Cell

Photoelectrochemical (PEC) seawater splitting is a promising method for the direct utilization of solar energy and abundant seawater resources for hydrogen production. Photoelectrodes are susceptible to various ions in seawater and complicated competitive reactions, resulting in the failure of photoelectrodes. This paper proposes the design and fabrication of different sputtered stainless steel (SS) films deposited on silicon photoanodes, completely isolating the electrolytes and semiconductor substrate. Upon coupling with the PEC flow cell, the back-illuminated photoanode coated with 316 SS cocatalyst achieves stable operation for 70 h in natural seawater with a highly alkaline KOH (30 wt.%, 7.64 mol/L) electrolyte due to the remarkable protection effect of the substrate from stainless steel, while the PEC seawater splitting system achieves a record hydrogen production rate of 600 μmol/(h·cm2). An appropriate Ni/Fe ratio in the SS ensures remarkable oxygen evolution activity, while chromic oxide ensures the effective anticorrosion effect by adjusting the microenvironment of the photoanodes. Moreover, fabricating PEC flow cells with photoanodes coated with SS cocatalysts are a viable strategy for PEC seawater splitting.

Tailoring the Chemical Environment of Ru–Mo Composites for Efficient Hydrogen and Oxygen Evolution Reactions

The development of cost‐effective and stable electrocatalysts that can replace the prevailing Pt‐based and Ir‐based catalysts for water splitting remains a formidable challenge. The electrocatalytic performance of a catalyst depends on its chemical composition and environment during catalysis. Herein, a Ru–Mo composite is used as an example to highlight the significance of tailoring the chemical environments of the active‐sites. This customization enhances the cathodic and anodic reactions involved in water splitting, ultimately leading to an improved full reaction efficiency. Specifically, the chemically reduced state of Ru–Mo demonstrates promising hydrogen evolution activity and exhibits low overpotentials of 48 and 34 mV at the current density of 10 mA cm−2 in acidic and alkaline electrolytes, respectively. The chemically oxidized state of Ru–Mo, derived from the same precursor, demonstrates proficient oxygen evolution activity and exhibits low overpotentials of 260 and 270 mV at 10 mA cm−2 in acidic and alkaline electrolytes, respectively. Additionally, in both cases, the Ru–Mo composites exhibit significantly improved stability under typical water‐splitting conditions. Despite the close chemical compositions of these two catalysts, they show poor performance in the counter electrode reactions, demonstrating the importance of establishing a suitable chemical environment for efficient electrocatalysis.

In-situ constructing oxide-anion dual-layer on Ce-B-containing electrode electrolyte interface towards highly corrosive seawater splitting

Seawater electrocatalysis holds significant promise as a technology for sustainable energy production, but the challenge of electrode corrosion by chloride ions is urgently needed to be addressed. Herein, a Ce-B-containing electrode was found to activate an in-situ evolutionary oxide (CeO2)-anion (B(OH)4–) dual-layer during the electrocatalytic reconstruction process, effectively resisting the invasion of chloride ions. In detail, a Ni-Fe-Ce-B electrode exhibits high hydrogen and oxygen evolution activity with only 160 and 271 mV overpotentials at 100 mA cm–2 in 1 M KOH + 0.5 M NaCl, and superior stability with slight overpotential loss after over 100 h at industrial current density ∼ 0.5 A cm–2 at 1.817 V for alkaline natural seawater splitting. Comparative experiments indicating that existing alkaline electrocatalysts can be adjusted to withstand rigorous seawater conditions through straightforward modifications. This work reveals a novel evolutionary oxide-anion dual-layer protection mechanism to effectively prevent chloride ion corrosion in highly corrosive seawater splitting.

Cooperative Fe sites on transition metal (oxy)hydroxides drive high oxygen evolution activity in base

Fe-containing transition-metal (oxy)hydroxides are highly active oxygen-evolution reaction (OER) electrocatalysts in alkaline media and ubiquitously form across many materials systems. The complexity and dynamics of the Fe sites within the (oxy)hydroxide have slowed understanding of how and where the Fe-based active sites form—information critical for designing catalysts and electrolytes with higher activity and stability. We show that where/how Fe species in the electrolyte incorporate into host Ni or Co (oxy)hydroxides depends on the electrochemical history and structural properties of the host material. Substantially less Fe is incorporated from Fe-spiked electrolyte into Ni (oxy)hydroxide at anodic potentials, past the nominally Ni2+/3+ redox wave, compared to during potential cycling. The Fe adsorbed under constant anodic potentials leads to impressively high per-Fe OER turn-over frequency (TOFFe) of ~40 s−1 at 350 mV overpotential which we attribute to under-coordinated “surface” Fe. By systematically controlling the concentration of surface Fe, we find TOFFe increases linearly with the Fe concentration. This suggests a changing OER mechanism with increased Fe concentration, consistent with a mechanism involving cooperative Fe sites in FeOx clusters.

Boosting the Oxygen Evolution Activity of FeNi Oxides/Hydroxides by Molecular and Atomic Engineering.

FeNi oxides/hydroxides are the best performing catalysts for oxidizing water at basic pH. Consequently, their improvement is the cornerstone to develop more efficient artificial photosynthetic systems. During the last 5 years different reports have demonstrated an enhancement of their activity by engineering their structures via: (1) modulation of the number of oxygen, iron and nickel vacancies; (2) single atoms (SAs) doping with metals such as Au, Ir, Ru and Pt; and (3) modification of their surface using organic ligands. All these strategies have led to more active and stable electrocatalysts for oxygen evolution rection (OER). In this Concept, we critically analyze these strategies using the most relevant examples.

Metal-organic framework-derived cation regulation of metal sulfides for enhanced oxygen evolution activity

Heteroatom doping serves as an important strategy to improve the oxygen evolution reaction (OER) activity of transition-metal compounds, while the investigation of intrinsic active sites and mechanisms remains insufficient. In this work, a facile cation regulation strategy is reported to boost the OER activity of metal sulfides via pyrolysis of the Ni-Co bimetallic metal-organic framework. The obtained Ni-substituted CoS nanoparticles on nitrogen-doped mesoporous carbon (Ni-CoS/NC) catalyst achieves a current density of 10 mA cm−2 at a small overpotential of 270 mV with a Tafel slope of 37 mV dec−1 in 1.0 mol L−1 KOH. Through a combination of spectroscopy study and theoretical computations, the activity origin is revealed at the atomic level. The CoxNi1–xOOH serves as the real active site for the OER generated by the Ni-CoS/NC reconstruction under oxidation potential during OER. The Ni substitution results in a strong electronic interaction between the two metals, thus generating more negatively charged Co atoms and more positively charged Ni atoms in the electrocatalyst. The metal sites with regulated electronic structure exhibit enhanced surface adsorption of OOH* and reduce the OER overpotential. Meanwhile, the conductive porous carbon scaffold facilitates electron transfer, mass diffusion, and the accessibility of active sites. This work not only provides a feasible cation regulation strategy for the design of high-performance electrocatalysts for low-cost energy storage and conversion systems, but also yields fresh insight into the activity enhancement mechanisms and intrinsic active sites.

Improvement of oxygen evolution activity on isolated Mn sites by dual-heteroatom coordination

The coordination of dual-heteroatom is an effective strategy to enhance the performance of oxygen evolution reaction (OER) of single-atom catalysts. Here, we synthesize Mn-SG-500 with isolated Mn sites coordinated with two sulfur and two oxygen atoms on graphene, and perform in-depth research on the structure-activity relationship for the OER. Under alkaline conditions, the Mn-SG-500 displays higher OER activity than commercial RuO2. Combining in-situ structure analysis and theoretical calculations, we identify Mn-S2O2 as the catalytic active center, on which the oxidation of *O to *OOH is the rate-control step. The improved OER activity is attributed to the redistribution and optimization of Mn charges caused by the co-coordination of S and O. This work is helpful for further structure design and performance management of single-atom catalysts with dual-heteroatom doping.

Tensile Strain-Mediated Spinel Ferrites Enable Superior Oxygen Evolution Activity.

Exploring efficient strategies to overcome the performance constraints of oxygen evolution reaction (OER) electrocatalysts is vital for electrocatalytic applications such as H2O splitting, CO2 reduction, N2 reduction, etc. Herein, tunable, wide-range strain engineering of spinel oxides, such as NiFe2O4, is proposed to enhance the OER activity. The lattice strain is regulated by interfacial thermal mismatch during the bonding process between thermally expanding NiFe2O4 nanoparticles and the nonexpanding carbon fiber substrate. The tensile lattice strain causes energy bands to flatten near the Fermi level, lowering eg orbital occupancy, effectively increasing the number of electronic states near the Fermi level, and reducing the pseudoenergy gap. Consequently, the energy barrier of the rate-determining step for strained NiFe2O4 is reduced, achieving a low overpotential of 180 mV at 10 mA/cm2. A total water decomposition voltage range of 1.52-1.56 V at 10 mA/cm2 (without iR correction) was achieved in an asymmetric alkaline electrolytic cell with strained NiFe2O4 nanoparticles, and its robust stability was verified with a voltage retention of approximately 99.4% after 100 h. Furthermore, the current work demonstrates the universality of tuning OER performance with other spinel ferrite systems, including cobalt, manganese, and zinc ferrites.