ChenDH

The inside chlorine ion substitution on layered Bi₄O₅Br₂ induces an 8‰ shrinkage of the halogen layer, triggering asymmetric [Bi₄O₅]²⁺ layer displacement polarization that significantly promotes charge separation. Meanwhile, the surface-substituted Cl ions activate the intrinsic redox dual-sites and are also self-donated as an alien oxidation site. These advantages collaboratively result in a remarkable efficiency in CO₂-to-CO photoreduction over Bi₄O₅Br₂.

Abstract

Sluggish bulk charge transfer and barren catalytic sites severely hinder the CO₂ photoreduction process. Seeking strategies for accelerating charge dynamics and activating reduction and oxidation sites synchronously presents a huge challenge. Herein, an inside-out chlorine (Cl) ions substitution strategy on the layered polar Bi₄O₅Br₂ is proposed for achieving layer structure-dependent polarization effect and redox dual-sites activation. Cl ions in the bulk phase shrink the halogen layer interspace by 8‰, triggering asymmetric [Bi₄O₅]²⁺ layer displacement polarization, prolonging the average photocharge lifetime to 201.8 ps. Meanwhile, surface substituted Cl ions enhance the electron-donating capability of neighboring Bi atoms, activating the intrinsic Bi reduction sites, and increasing H₂O molecule adsorption on nearby intrinsic O oxidation site (cal. by 0.105 eV), also self-donating as an alien oxidation site. Besides, Cl upshifts the p-band center closer to the Fermi level, facilitating the reactant adsorption. Therefore, the energy barrier for CO₂ activation and rate-limiting ^*COOH intermediate formation steps are significantly decreased. Without cocatalysts and sacrificial reagents, inside-out Cl-substituted Bi₄O₅Br₂ delivers a remarkable CO₂-to-CO photoreduction rate of 50.18 µmol g⁻¹ h⁻¹, being one of the state-of-the-art catalysts. This finding offers insights into exploiting polarization at the molecular-level and enhances understanding of catalytic site activation.

This research reports a nickel-doped copper nanowire catalyst for highly selective ethanol production from CO electroreduction. The theoretical calculations and operando spectroelectrochemical investigations cooperatively demonstrate that nickel-doping onto copper surface can regulate the interfacial water structure and water dissociation kinetics, which significantly influences the hydrogenation kinetics of a key C₂ intermediate (^*CHCOH), and thus leading to a high selectivity switch from ethylene to ethanol.

Abstract

Ethanol isa promising energy vector for closing the anthropogenic carbon cycle through reversible electrochemical redox. Currently, ethanol electrosynthesissuffers from low product selectivity due to the competitive advantage of ethylene in CO₂/CO electroreduction. Here, a facet-selective metal-doping strategy is reported, tuning the reaction kinetics of CO reduction paths and thus enhancing the ethanol selectivity. The theoretical calculations reveal that nickel (Ni)doped Cu(100) surface facilitates water dissociation to form adsorbed hydrogen, which promotesselective electrochemical hydrogenation of a key C₂ intermediate (^*CHCOH) toward ethanol path over ethylene path. Experimentally, a solution-phase synthesis of a Ni-doped {100}-dominated Copper nanowires (Cu NWs) catalyst is reported, enabling an ethanol Faradaic efficiency of 56% and a selectivity ratio of ethanol to ethylene of 2.7, which are ≈4 and 15 times larger than those of undoped Cu NWs, respectively. The operando spectroscopic characterizations confirm that Ni-doping in Cu NWs can alter the interfacial water activity and thus regulate the C₂ product selectivity. With further electrode engineering, a membrane electrode assembly electrolyzer using Ni-doped Cu NWs catalysts demonstrates an ethanol Faradaic efficiency over 50% at 300 mA cm⁻² with a full cell voltage of ≈2.7 V and operates stably for over 300 h.

It is unveiled that oxygen-containing groups connect the unsaturated aliphatic hydrocarbon and aromatic side chains to form disordered carbon skeleton to inhibit metlting and rearrangement during carbonization. The simultaneous increase in initial coulombic efficiency, capacity and tansport behavior of sodium ions in hard carbons are achieved by adjusting the carbon layer and micropore. Besides, the “adsorption-insertion-pores-filling” sodium storage mechanism is proposed.

Abstract

Because direct carbonation of asphalt usually yields ordered graphite structure with unfavorable storage of sodium. Here, the asphalt preoxidation at a specific temperature in the air introduces oxygen-containing groups to connect the unsaturated aliphatic hydrocarbon and aromatic side chains, forming a disordered carbon skeleton to inhibit melting and rearrangement during carbonization. The abundant oxygen-containing groups hinder the growth of the carbon layers during pyrolysis, which promotes the formation of disordered phases and abundant micropores in asphalt-based hard carbons (HCs). The simultaneous increase in initial coulombic efficiency, capacity, and transport behavior of sodium ions in HCs is achieved by adjusting the carbon layer and micropore evolution. The optimized HCs display excellent initial coulombic efficiency of 86.14% with remarkable reversible capacity of 313.83 mAh g⁻¹ at 0.1 C and high-rate capability with 140 mAh g⁻¹ at 5 C. Pairing with O3-NaNi_1/3Fe_1/3Mn_1/3O₂ cathode, the full cell delivers a higher reversible capacity of 255.7 mAh g⁻¹ with an initial coulombic efficiency of 83.7% and long cycle life. Based on the microstructure and electrochemical behaviors of asphalt-based HCs, the “adsorption-insertion-pores-filling” sodium storage mechanism is proposed, providing guidelines for designing high-energy-density sodium-ion batteries.

This review summarizes state-of-art of coupled electrolyzers, the integration of oxidation reactions of small molecules (including sacrificial agent oxidation reaction and electrochemical synthesis reaction with reduction reactions including hydrogen evolution reaction, oxygen reduction reaction, CO₂ reduction reaction, and N₂ reduction reaction. Current challenges and prospects of this appealing strategy are discussed and outlined.

Abstract

Coupled electrolyzer is a desirable way to realize efficient energy conversion from electricity to chemical energy. Using coupled electrolyzers highly valuable chemicals (e.g., H₂, CH _x COO⁻, nitrile, S, NH₃, CO) can be obtained at low voltages, environmental pollutants can be alleviated, and wastewater (e.g., ammonia, urea, hydrazine) can be recycled. They are even helpful to realize the goal of carbon peaking and carbon neutrality. Compared to traditional chemical methods, small molecule-based coupled electrolyzers are more cost-efficient. This review summarizes state-of-art of coupled electrolyzers, mainly the replacement of oxygen reduction reaction with oxidation reactions of small molecules and their further coupling with cathodic reduction reactions such as hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), CO₂ reduction reaction (CO₂RR), N₂ reduction reaction (NRR), and other reduction reactions of matching small molecules. In terms of oxidation reactions of small molecules, two types of reactions are covered: sacrificial agent oxidation reaction (SAOR) and electrochemical synthesis reaction (ESR). After detailing the design principle of coupled electrolyzers and several oxidation reactions of small molecules, construction, characterization, and performance of coupled electrolyzers are systematically overviewed along with discussion and outline of current challenges and prospects of this appealing strategy.

This study reveals that incorporating copper into a double perovskite structure is challenging, as Cs₂CuBiCl₆ does not form under the same experimental conditions, leading to copper acting as interstitial dopants in the pristine Cs₃Bi₂Cl₉ structure. Copper incorporation significantly enhances CO₂ photoreduction activity, with transient absorption results showing increased carrier generation and elevated carrier decay lifetime in Cu-Cs₃Bi₂Cl₉.

Abstract

Double perovskite have attracted substantial attention as prospective materials for applications in optoelectronics and photocatalysis. Significant efforts are devoted to modulating the properties of double perovskites to improve their performance. One promising approach involves substituting silver (Ag) with copper (Cu), which offers favorable electronic characteristics. Despite promising theoretical predictions, the experimental synthesis of copper-based double perovskites has presented notable challenges. Here, the challenges of Cu incorporation in double perovskites and the subsequent – impact of Cu on the photocatalytic activity of halide perovskites toward CO₂ reduction are explored. Combining detailed computational thermodynamic studies, it is found that Cu does not form the traditional double perovskite structure that is Cs₂CuBiCl₆; it stays as an interstitial dopant in its pristine Cs₃Bi₂Cl₉ structure. The Cu-Cs₃Bi₂Cl₉ are found to exhibit enhanced CO₂ photoreduction activity than the pristine Cs₃Bi₂Cl₉. Further, transient absorption results show that Cu dopants enhance the carrier generation because of introduced sub-bandgap states, and it is found that carrier decay lifetime is elevated in Cu-Cs₃Bi₂Cl₉, which can enhance the participation of carriers in CO₂ photoreduction. The study explores the challenges and opportunities of copper doping in halide perovskites, offering the potential for developing efficient CO₂ reduction photocatalysts.

The use of double-hollow Au@CdS yolk@shell nanostructures as plasmonic photocatalysts for solar hydrogen production is demonstrated. The apparent quantum yield of hydrogen production can reach 8.2% at 320 nm, 6.2% at 420 nm, and 4.4% at 660 nm. The plasmon-enhanced activity at 660 nm is exceptional, surpassing the plasmon-induced photoactivities of the state-of-the-art plasmonic photocatalysts ever reported.

Abstract

Structural engineering has proven effective in tailoring the photocatalytic properties of semiconductor nanostructures. In this work, a sophisticated double-hollow yolk@shell nanostructure composed of a plasmonic, mobile, hollow Au nanosphere (HGN) yolk and a permeable, hollow CdS shell is proposed to achieve remarkable solar hydrogen production. The shell thickness of HGN@CdS is finely adjusted from 7.7, 18.4 to 24.5 nm to investigate its influence on the photocatalytic performance. Compared with pure HGN, pure CdS, a physical mixture of HGN and CdS, and a counterpart single-hollow cit-Au@CdS yolk@shell nanostructure, HGN@CdS exhibits superior hydrogen production under visible light illumination (λ = 400–700 nm). The apparent quantum yield of hydrogen production reaches 8.2% at 320 nm, 6.2% at 420 nm, and 4.4% at 660 nm. The plasmon-enhanced activity at 660 nm is exceptional, surpassing the plasmon-induced photoactivities of the state-of-the-art plasmonic photocatalysts ever reported. The superiority of HGN@CdS originates from the creation of charge separation state at HGN/CdS heterojunction, the considerably long-lived hot electrons of plasmonic HGN, the magnified electric field, and the advantageous features of double-hollow yolk@shell nanostructures. The findings can provide a guideline for the rational design of versatile double-hollow yolk@shell nanostructures for widespread photocatalytic applications.

FeSe₂ nanoparticles are successfully encapsulated in phosphorus-doped mesoporous carbon (PMC) armed by graphene aerogel (GA) (GA@PMC) to prepare a FeSe₂/GA@PMC composite. Compared with bare PMC, the GA@PMC composite can provide enhanced electroconductivity, rapid Na⁺/electrolyte diffusion channels, decreased surface areas, and more integrated and stable structure. As expect, FeSe₂/GA@PMC electrode demonstrates superior electrochemical performance in Na-ion based energy storage devices.

Abstract

The rise of Na-storage devices has put forward higher requirements for Na-storage anode materials with large capacity, long service life, and fast rate capability. Mesoporous carbons, either as active materials or as hosts for guest active nanoparticles, are considered as promising electrode materials. However, addressing the issues of their short lifespan resulting from volume variation and the low coulombic efficiency caused by large surface area via a facile porous structure design still remains a challenge. Herein, a versatile phosphorus-doped mesoporous carbon (PMC) armed is developed by graphene aerogel (GA) (GA@PMC) for hosting Na-storage active nanoparticles. As a case study, FeSe₂ nanoparticles are selectively supported onto this GA@PMC matrix, creating the FeSe₂/GA@PMC composite. When employed in typical Na-storage devices, such as Na-ion batteries, Na-ion hybrid capacitors, and Na-ion based dual-ion batteries, the FeSe₂/GA@PMC electrode consistently demonstrates superior electrochemical performance. In such GA@PMC, the conformal GA can improve the entire conductivity while decreasing the specific surface area that is directly contacting with electrolyte. The interconnected macroporous structure can not only promote the diffusion of Na⁺ but also buffers the volume change of the guest active nanoparticles. This bespoke carbon platform synergistically endows the electrode material with enhanced rate capability, cyclic stability, and coulombic efficiency, which are being expected in advanced Na-storage devices.

Comparative analysis summarizes the impact of various ion irradiation parameters (mass, energy, incident angle) on defect formation in supported and freestanding 2D materials. Supported materials exhibit consistently higher defect numbers, attributed to the significant impact of the substrate, which introduces extra defect production due to backscattered ions and sputtered atoms.

Abstract

Understanding the nature, density, and distribution of structural defects is crucial for tailoring the properties of atomically thin two-dimensional (2D) materials, which is paramount for advances in nanotechnology. Ion irradiation emerges as a promising technique for defect engineering of single-atom-thick materials, due to its high controllability, repeatability, and accuracy. The objective is to provide a comprehensive review elucidating the impact of various irradiation parameters, such as ion mass, energy, fluence, and incident angle, on defect formation in 2D materials. However, the presence of the substrate can significantly influence defect yield and the mechanism of formation due to backscattered ions and sputtered substrate atoms. Hence, a thorough comparison of ion beam-induced defects in both freestanding (suspended) and supported (on a substrate) 2D materials, with a focus on substrate effects is conducted. Moreover, a detailed analysis of characterization techniques suitable for each scenario will be provided. This work not only contributes to advancing the current understanding of defect formation and evolution in 2D materials during ion beam irradiation but also offers insights into selecting specific parameters for this process to create desired defects in these materials. Consequently, it has the potential to facilitate the design of nanoscale devices with tailored functionality.

The dual doping of B and Fe can significantly enhance the oxygen evolution reaction (OER) activity by efficiently shifting the OER pathway of restructured oxyhydroxides from the conventional adsorbate evolution mechanism to lattice oxygen mechanism, compared to doping with B or Fe alone. The optimized B, Fe─CoP nanofibers only require low overpotentials of 361 and 376 mV at 1000 mA cm^-2 in alkaline freshwater and alkaline natural seawater, respectively.

Abstract

The exploitation of highly activity oxygen evolution reaction (OER) electrocatalysts is critical for the application of electrocatalytic water splitting. Triggering the lattice oxygen mechanism (LOM) is expected to provide a promising pathway to overcome the sluggish OER kinetics, however, effectively enhancing the involvement of lattice oxygen remains challenging. In this study, the fabrication of B, Fe co-doped CoP (B, Fe─CoP) nanofibers is reported, which serve as highly efficient OER electrocatalyst through phosphorization and boronation treatment of Fe-doped Co₃O₄ nanofibers. Experimental results combined with theoretical calculations reveal that simultaneous incorporation of both B and Fe can more effectively trigger the participation of lattice oxygen in CoFe oxyhydroxides reconstructed from B, Fe─CoP nanofibers compared to incorporating only B or Fe. Therefore, the optimized B, Fe─CoP nanofibers exhibit superb OER activity with low overpotentials of 361 and 376 mV at 1000 mA cm⁻² in alkaline freshwater and alkaline natural seawater, respectively. The present work provides significant guidelines and innovative design concepts for the development of OER electrocatalysts following the LOM pathway.

This review provides a comprehensive summary of niobium-based anode materials, including synthesis strategy, structural design, and their applications in alkali metal-ion batteries. An in-depth insight into the structure-performance correlation is given, and rational design concepts and future development directions specifically tailored to fast-charging applications are also highlighted, aiming at broadening the advanced energy storage applications of niobium-based materials.

Abstract

The rapid advancement of clean energy has aroused an increased demand for advanced energy storage systems. Alkali metal-ion batteries (AMIBs) including lithium/sodium/potassium-ion batteries (LIBs/SIBs/PIBs) play a crucial role in these systems, and their development is closely related to the progress of electrode materials. Niobium (Nb)-based materials exhibit distinctive features such as quasi-2D framework, high intercalation potential, robust pseudo-capacitance effect, and minimal volume expansion during cycles. These characteristics render them highly valuable for energy storage applications. However, the low conductivity and limited capacity of Nb-based electrode materials significantly limit their widespread development in energy storage applications. To address these challenges, various strategies have been explored. This review primarily summarizes the recent advancements in research on Nb-based anode materials for AMIBs over the past decade. The synthesis strategy, structure design, and material composite of Nb-based materials are systematically discussed, and the performances of different types of batteries are also well analyzed and compared. Meanwhile, their merits in the fast-charging realm are then highlighted. Importantly, this review presents the key issues and challenges encountered by Nb-based anode materials in future energy storage, along with novel concepts and solutions for the research and development of next-generation Nb-based anodes.

A multiscale hierarchical porous micro-sized germanium (p-Ge) comprising of interconnected nano-ligaments and bicontinuous nanopores is rationally designed by an innovative double template dealloying method. This design enables the resultant p-Ge anode with alleviated volume variation, high tap density, high activity, and decreased Li⁺ diffusion distance demonstrating superior Li- storage performance in terms of initial Coulombic efficiency, volumetric capacity, and long-term stability.

Abstract

The manipulation of stress in high-capacity microscale alloying anode materials, which undergo significant volumetric variation during cycling, is crucial prerequisite for improved their cycling capability. In this work, an innovative structural design strategy is proposed for scalable fabrication of a unique 3D highly porous micro structured germanium (Ge) featuring micro-nano hierarchical architecture as viable anode for high-performance lithium-ion batteries (LIBs). The resultant micro-sized Ge, consisting of interconnected nanoligaments and bicontinuous nanopores, is endowed with high activity, decreased Li⁺ diffusion distance and alleviated volume variation, appealing as an ideal platform for in-depth understanding the relationship between structural design and stress evolution. Such a micro-sized Ge being highly porous delivers a record high initial Coulombic efficiency of 92.5%, large volumetric capacity of 2,421 mAh cm⁻³ at 1.2 mA cm⁻², exceptional rate capability (805.6 mAh g⁻¹ at 10 Ag⁻¹) and cycling stability (over 90% capacity retention after 1000 cycles even at 5 A g⁻¹), largely outperforming the reported Ge-based anodes for LIBs. Furthermore, its underlying Li storage mechanism and stress dispersion behavior are explicitly revealed by combined substantial in situ/ex situ experimental characterizations and theoretical computation. This work provides novel insights into the rational design of high-performance and durable alloying anodes toward high-energy LIBs.

Highly active oxygen evolution reaction electrocatalysts, such as those containing Fe, often face the challenge of severe dissolution of active elements. Here, the correlation between precatalyst structural changes and interfacial dynamic stability is elucidated by investigating the structural evolution of Fe-containing Prussian blue analogs.

Abstract

Highly active oxygen evolution reaction (OER) electrocatalysts, such as those containing Fe, often face the challenge of severe dissolution of active elements. Addressing this concern through the establishment of a dynamically stable interface during OER presents a promising strategy, achieved by manipulation of catalyst components. Herein, the findings reveal that Fe loss during OER predominantly occurs during the initial activation phase, marked by irreversible structural distortion that disrupts interfacial dynamical stability. By investigating the structural evolution of Fe-containing Prussian blue analogs, serving as a model OER precatalyst, the correlation between precatalyst structural changes and interfacial dynamic stability is elucidated. Utilizing thermal annealing of CoFe bimetal Prussian blue, favorable thermodynamic conditions are induced for generating cyano vacancies within the matrix, thereby facilitating enhanced initial activation during OER. Consequently, catalytically active and stable oxyhydroxide species rapidly form at the interface, exhibiting robust interactions with interfacial Fe elements to stabilize interface dynamics. Suppression of the irreversible structural distortion responsible for active element loss during initial activation culminates in enhanced OER activity and stability.

The metal–organic framework based heterogeneous electrocatalysts (MOF-on-MOF) can facilitate electron transfer at the dual-MOF interface. In addition, the synergistic effect between Ni and Fe sites can promote electronic structure reconfiguration of active sites. Based on the above strategies for modulating the electronic structure of MOF-based electrocatalysts, MOF-(74 + 274)@NFF with optimal electronic structure exhibits superior oxygen evolution reaction (OER) performance.

Abstract

Electron modulation presents a captivating approach to fabricate efficient electrocatalysts for the oxygen evolution reaction (OER), yet it remains a challenging undertaking. In this study, an effective strategy is proposed to regulate the electronic structure of metal–organic frameworks (MOFs) by the construction of MOF-on-MOF heterogeneous architectures. As a representative heterogeneous architectures, MOF-74 on MOF-274 hybrids are in situ prepared on 3D metal substrates (NiFe alloy foam (NFF)) via a two-step self-assembly method, resulting in MOF-(74 + 274)@NFF. Through a combination of spectroscopic and theory calculation, the successful modulation of the electronic property of MOF-(74 + 274)@NFF is unveiled. This modulation arises from the phase conjugation of the two MOFs and the synergistic effect of the multimetallic centers (Ni and Fe). Consequently, MOF-(74 + 274)@NFF exhibits excellent OER activity, displaying ultralow overpotentials of 198 and 223 mV at a current density of 10 mA cm⁻² in the 1.0 and 0.1 M KOH solutions, respectively. This work paves the way for manipulating the electronic structure of electrocatalysts to enhance their catalytic activity.

In this perspective, several impacts of anodic oxidation of liquid products in terms of performance evaluation, e.g., misestimation of the Faradaic efficiency, are elaborated. It is revealed that dynamic change of the anolyte (i.e., pH and composition) not only brings a shift of anodic potentials, but also affects the chemical stability of the anode catalyst.

Abstract

The membrane-electrode assembly (MEA) approach appears to be the most promising technique to realize the high-rate CO₂/CO electrolysis, however there are major challenges related to the crossover of ions and liquid products from cathode to anode via the membrane and the concomitant anodic oxidation reactions (AORs). In this perspective, by combining experimental and theoretical analyses, several impacts of anodic oxidation of liquid products in terms of performance evaluation are investigated. First, the crossover behavior of several typical liquid products through an anion-exchange membrane is analyzed. Subsequently, two instructive examples (introducing formate or ethanol oxidation during electrolysis) reveals that the dynamic change of the anolyte (i.e., pH and composition) not only brings a slight shift of anodic potentials (i.e., change of competing reactions), but also affects the chemical stability of the anode catalyst. Anodic oxidation of liquid products can also cause either over- or under-estimation of the Faradaic efficiency, leading to an inaccurate assessment of overall performance. To comprehensively understand fundamentals of AORs, a theoretical guideline with hierarchical indicators is further developed to predict and regulate the possible AORs in an electrolyzer. The perspective concludes by giving some suggestions on rigorous performance evaluations for high-rate CO₂/CO electrolysis in an MEA-based setup.

An azide-functionalized cobaloxime proton-reduction catalyst covalently tethered into the Wurster-type covalent organic frameworks is developed for achieving the enhanced photocatalytic activity for hydrogen evolution in alcohol-containing solutions without any sacrificial agent.

Abstract

We report an azide-functionalized cobaloxime proton-reduction catalyst covalently tethered into the Wurster-type covalent organic frameworks (COFs). The cobaloxime-modified COF photocatalysts exhibit enhanced photocatalytic activity for hydrogen evolution reaction (HER) in alcohol-containing solution with no presence of a typical sacrificial agent. The best performing cobaloxime-modified COF hybrid catalyzes hydrogen production with an average HER rate up to 38 μmol h⁻¹ in ethanol/phosphate buffer solution under 4 h illumination. Ultrafast transient optical spectroscopy characterizations and charge carrier analysis reveal that the alcohol contents functioning as hole scavengers could be oxidized by the photogenerated holes of COFs to form aldehydes and protons. The consumption of the photogenerated holes thus suppresses exciton recombination of COFs and improves the ratio of free electrons that were effectively utilized to drive catalytic reaction for HER. This work demonstrates a great potential of COF-catalyzed HER using alcohol solvents as hole scavengers and provides an example toward realizing the accessibility to the scope of reaction conditions and a greener route for energy conversion.

Nanoflower-like carbon-encapsulated CoNiPt catalyst with composition segregation (CoNi-rich and Pt-rich) is obtained by pyrolyzing MOF precursors. These segregation alloy components synergically promote the kinetic activity of alkaline hydrogen evolution reaction (HER). This work provides novel insights into the design of efficient and low-cost alkaline HER catalyst derived from metal–organic frameworks by coordinating kinetic reaction sites at segregation alloy and adopting the appropriate drying process.

Abstract

Constructing an efficient alkaline hydrogen evolution reaction (HER) catalyst with low platinum (Pt) consumption is crucial for the cost reduction of energy devices, such as electrolyzers. Herein, nanoflower-like carbon-encapsulated CoNiPt alloy catalysts with composition segregation are designed by pyrolyzing morphology-controlled and Pt-proportion-tuned metal–organic frameworks (MOFs). The optimized catalyst containing 15% CoNiPt NFs (15%: Pt mass percentage, NFs: nanoflowers) exhibits outstanding alkaline HER performance with a low overpotential of 25 mV at a current density of 10 mA cm⁻², far outperforming those of commercial Pt/C (47 mV) and the most advanced catalysts. Such superior activity originates from an integration of segregation alloy and Co-O hybridization. The nanoflower-like hierarchical structure guarantees the full exposure of segregation alloy sites. Density functional theory calculations suggest that the segregation alloy components not only promote water dissociation but also facilitate the hydrogen adsorption process, synergistically accelerating the kinetics of alkaline HER. In addition, the activity of alkaline HER is volcanically distributed with the surface oxygen content, mainly in the form of Co_3dO_2p hybridization, which is another reason for enhanced activity. This work provides feasible insights into the design of cost-effective alkaline HER catalysts by coordinating kinetic reaction sites at segregation alloy and adjusting the appropriate oxygen content.

Solar thermoelectric generators are thermoelectric devices that utilize solar radiation to increase the temperature at the heat source of the device and generate electrical power. This review describes different designs of solar thermoelectric generators within the context of thermoelectric elements, optical concentrators, solar absorbers, and other techniques to enhance their output performance.

Abstract

Thermoelectric materials convert waste heat into electricity, making sustainable power generation possible when a temperature gradient is applied. Solar radiation is one potential abundant and eco-friendly heat source for this application, where one side of the thermoelectric device is heated by incident sunlight, while the other side is kept at a cooler temperature. This is known as solar thermoelectric generation. Various thermoelectric materials are used for different solar thermoelectric applications, and different methods are explored to enhance the temperature gradient across the material. Solar optical concentrators, thermal and selective absorbers, and other tools are proposed to improve the performance of solar thermoelectrics. Despite continuous research and development, experimental solar thermoelectric efficiencies remain below 10%, and theoretical efficiencies do not surpass 20%. In this review, the different designs of solar thermoelectric generators are examined within the context of thermoelectric elements, optical concentrators, solar absorbers, and other techniques to enhance their performance. Last, an overview of the current state of solar thermoelectrics is provided, areas for improvement are suggested, and the future of these devices is predicted.

The photoelectrochemical oxygen evolution reaction (OER) at semiconductor electrodes is a highly complex multielectron transfer process that commonly requires large potential bias to minimize competing interfacial recombination losses. Herein, for the first time, it is shown that polycrystalline GaFeO₃, a highly ionic n‐type ferrite with very positive band edges, can promote the OER without external bias.

Abstract

The photoelectrochemical properties of polycrystalline GaFeO₃ (GFO) thin films are investigated for the first time. Thin films prepared by sol–gel methods exhibit phase‐pure orthorhombic GFO with the Pc21n space group, as confirmed by X‐ray diffraction and Raman spectroscopy. Optical responses are characterized by a 2.72 eV interband transition and sub‐bandgap d–d transitions associated with octahedral and tetrahedral coordination of Fe³⁺ sites. DFT‐HSE06 electronic structure calculations show GFO is highly ionic with very low dispersion in the valence band maximum (VBM) and conduction band minimum (CBM). Electrochemical impedance spectroscopy reveals n‐type conductivity with a flat band potential (U _fb) of 0.52 V versus reversible hydrogen electrode, indicating that GFO has the most positive CBM reported of any ferrite. The photoelectrochemical oxidation of SO₃ ²⁻ shows an ideal semiconductor–electrolyte interfacial behavior with no evidence of surface recombination down to the U _fb. Surprisingly, the onset potential for the oxygen evolution reaction also coincides with the U _fb, showing interfacial hole‐transfer efficiency above 50%. The photoelectrochemical properties are limited by bulk recombination due to the short‐diffusion length of minority carriers as well as slow transport of majority carriers. Strategies towards developing high‐efficiency GFO photoanodes are briefly discussed.

Publication date: 1 May 2019

Source: Journal of Power Sources, Volume 421

Author(s): Peng Xu, Hao Xu, Dayang Zheng

Graphical abstract