Hydrogen, a new energy carrier that can replace traditional fossil fuels, is seen as one of the most promising clean energy sources. The use of renewable electricity to drive hydrogen production has ...very broad prospects for addressing energy and environmental problems. Therefore, many researchers favor electrolytic water due to its green and low‐cost advantages. The electrolytic water reaction comprises the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Understanding the OER and HER mechanisms in acidic and alkaline processes contributes to further studying the design of surface regulation of electrolytic water catalysts. The OER and HER catalysts are mainly reviewed for defects, doping, alloying, surface reconstruction, crystal surface structure, and heterostructures. Besides, recent catalysts for overall water splitting are also reviewed. Finally, this review paves the way to the rational design and synthesis of new materials for highly efficient electrocatalysis.
Hydrogen production driven by renewable electricity has very broad prospects for addressing energy and environmental problems. This review provides in‐depth discussions on the mechanisms of water electrolysis and water electrolyzers. Furthermore, the surface regulation strategies of catalysts, including defects, doping, alloying, surface reconstruction, crystal surface structure, and heterostructures are presented.
Hydrogen peroxide is a highly valuable chemical, and electrocatalytic oxygen reduction towards H2O2 offers an alternative method for safe on‐site applications. Generally, low‐cost hematite (α‐Fe2O3) ...is not recognized as an efficient electrocatalyst because of its inert nature, but it is herein reported that α‐Fe2O3 can be endowed with high catalytic activity and selectivity via the engineering of facets and oxygen vacancies. Density‐functional theory (DFT)calculations predict that the {001} facet is intrinsically selective for H2O2 production, and that oxygen vacancies can trigger the high activity, providing sites for O2 adsorption and protonation, stabilizing the *OOH intermediate, and preventing cleavage of the OO bond. The synthesized oxygen‐defective α‐Fe2O3 single crystals with exposed {001} facets achieve high selectivities for H2O2 of >90%, >88%, and >95% in weakly acidic, neutral, and alkaline electrolytes, respectively, and the H2O2 production rate reaches 454 mmol g−1cat h−1 at 0.1 V versus RHE under alkaline conditions. In an anion exchange membrane fuel cell, a maximum H2O2 production of 546.8 mmol L−1 with a high Faradaic efficiency of 80.5% is achieved. Thus, this work details a low‐cost catalyst feasible for H2O2 synthesis, and highlights the feasibility of theoretical catalyst design for practical applications.
Facet and oxygen vacancy engineering endow hematite with high activity and selectivity for electrocatalytic oxygen reduction to H2O2 over a wide pH range, which represents a promising low‐cost electrocatalyst for H2O2 synthesis and demonstrates the feasibility of theoretical catalyst design for practical applications.
Solar‐driven water splitting is in urgent need for sustainable energy research, for which accelerating oxygen evolution kinetics along with charge migration is the key issue. Herein, Mn3+ within ...π‐conjugated carbon nitride (C3N4) in form of Mn–N–C motifs is coordinated. The spin state (eg orbital filling) of Mn centers is regulated by controlling the bond strength of Mn–N. It is demonstrated that Mn serves as intrinsic oxygen evolution reaction (OER) site and the kinetics is dependent on its spin state with an optimized eg occupancy of ≈0.95. Specifically, the governing role of eg occupancy originates from the varied binding strength between Mn and OER intermediates. Benefiting from the rapid spin state‐mediated OER kinetics, as well as extended optical absorption (to 600 nm) and accelerated charge separation by intercalated metal‐to‐ligand state, Mn–C3N4 stoichiometrically splits pure water with H2 production rate up to 695.1 µmol g−1 h−1 under simulated sunlight irradiation (AM1.5), and achieves an apparent quantum efficiency of 4.0% at 420 nm, superior to most solid‐state based photocatalysts to date. This work for the first time correlates photocatalytic redox kinetics with the spin state of active sites, and suggests a nexus between photocatalysis and spin theory.
Highly active oxygen‐evolving Mn3+ centers are incorporated into photoresponsive carbon nitride (C3N4) as Mn–N–C motif for solar‐driven water splitting. For the first time, the spin state of Mn is tuned to boost oxygen evolution with an optimized eg≈0.95 occupancy. The extended optical absorption, accelerated charge migration, and spin‐mediated fast redox kinetics endow Mn–C3N4 with superior activity.
The conversion, storage, and utilization of renewable energy have all become more important than ever before as a response to ever‐growing energy and environment concerns. The performance of ...energy‐related technologies strongly relies on the structure and property of the material used. The earth‐abundant family of tungsten oxides (WOx≤3) receives considerable attention in photocatalysis, electrochemistry, and phototherapy due to their highly tunable structures and unique physicochemical properties. Great breakthroughs have been made in enhancing the optical absorption, charge separation, redox capability, and electrical conductivity of WOx≤3 through control of the composition, crystal structure, morphology, and construction of composite structures with other materials, which significantly promotes the efficiency of processes and devices based on this material. Herein, the properties and synthesis of WOx≤3 family are reviewed, and then their energy‐related applications are highlighted, including solar‐light‐driven water splitting, CO2 reduction, and pollutant removal, electrochromism, supercapacitors, lithium batteries, solar and fuel cells, non‐volatile memory devices, gas sensors, and cancer therapy, from the aspect of function‐oriented structure design and control.
Recent breakthroughs on structure control and modification of the WOx≤3 family for energy‐related applications are summarized, including for solar‐light‐driven water splitting, CO2 reduction, pollutant removal, electrochromism, supercapacitors, lithium batteries, solar and fuel cells, non‐volatile memory devices, gas sensors, and cancer therapy, from the aspects of function‐oriented structure design and control.
Proton exchange membrane water electrolyzer (PEMWE) technology is of interest in the context of electrocatalytic hydrogen generation from renewable energies. It has the benefits of immediate ...response, higher proton conductivity, lower ohmic losses, and gas crossover rate. One key step toward to large‐scale application, is the development of highly efficient, durable, and compatible anodic oxygen evolution electrocatalysts in acidic media to decrease the usage of expensive and scarce precious metals. Within this scenario, an in‐depth understanding of oxygen evolution reaction mechanisms including the adsorption evolution mechanism and lattice oxygen evolution mechanism is first provided to aid development of innovative materials and elucidate the origin of catalyst degradation. Second, recent progress in the development of oxygen evolution electrocatalysts in acid media is reviewed with an emphasis on the underlying structure–performance relationships. Third, the current application status and research progress in PEMWEs along with representative examples are discussed. Last, the remaining challenges and promising insights are proposed to inspire future studies on the development of hydrogen production technology from renewable energy.
This timeline demonstrates major developments in the application and theory for water electrolysis since its discovery. Vigorous development implies that water electrolysis promises to be a major force to promote the realization of clean energy production in human society. The accelerating pace of technological theory updates calls for timely and comprehensive reviews for both fundamental scientific research and practical applications.
Direct conversion of solar light into chemical energy by means of photocatalysis or photoelectrocatalysis is currently a point of focus for sustainable energy development and environmental ...remediation. However, its current efficiency is still far from satisfying, suffering especially from severe charge recombination. To solve this problem, the piezo‐phototronic effect has emerged as one of the most effective strategies for photo(electro)catalysis. Through the integration of piezoelectricity, photoexcitation, and semiconductor properties, the built‐in electric field by mechanical stimulation induced polarization can serve as a flexible autovalve to modulate the charge‐transfer pathway and facilitate carrier separation both in the bulk phase and at the surfaces of semiconductors. This review focuses on illustrating the trends and impacts of research based on piezo‐enhanced photocatalytic reactions. The fundamental mechanisms of piezo‐phototronics modulated band bending and charge migration are highlighted. Through comparing and classifying different categories of piezo‐photocatalysts (like the typical ZnO, MoS2, and BaTiO3), the recent advances in polarization‐promoted photo(electro)catalytic processes involving water splitting and pollutant degradation are overviewed. Meanwhile the optimization methods to promote their catalytic activities are described. Finally, the outlook for future development of polarization‐enhanced strategies is presented.
The piezo‐phototronic effect enables the engineering of charge‐carrier characteristics at both heterojunction interfaces and the bulk phase, and provides a driving force for the transport of photoinduced charges in specific directions. This review focuses on the advanced polarization‐promoted processes involving water splitting and pollutant degradation.
Hydrogen evolution reaction (HER) in alkaline medium is currently a point of focus for sustainable development of hydrogen as an alternative clean fuel for various energy systems, but suffers from ...sluggish reaction kinetics due to additional water dissociation step. So, the state‐of‐the‐art catalysts performing well in acidic media lose considerable catalytic performance in alkaline media. This review summarizes the recent developments to overcome the kinetics issues of alkaline HER, synthesis of materials with modified morphologies, and electronic structures to tune the active sites and their applications as efficient catalysts for HER. It first explains the fundamentals and electrochemistry of HER and then outlines the requirements for an efficient and stable catalyst in alkaline medium. The challenges with alkaline HER and limitation with the electrocatalysts along with prospective solutions are then highlighted. It further describes the synthesis methods of advanced nanostructures based on carbon, noble, and inexpensive metals and their heterogeneous structures. These heterogeneous structures provide some ideal systems for analyzing the role of structure and synergy on alkaline HER catalysis. At the end, it provides the concluding remarks and future perspectives that can be helpful for tuning the catalysts active‐sites with improved electrochemical efficiencies in future.
In this review, recent progress and solutions to the challenges associated with electrocatalysts for hydrogen evolution reaction (HER) in alkaline electrolytes are systematically explained. It further describes the reaction controlling factors and ambiguity of the alkaline HER process and outlines the possible ways to enhance the catalyst efficiency and stability. By modifying the electronic structure of catalysts through developing their heterostructures can overcome the water dissociation barrier to realize alkaline HER.
Photocatalysis has been regarded as a promising strategy for hydrogen production and high-value-added chemicals synthesis, in which the activity of photocatalyst depends significantly on their ...electronic structures, however the effect of electron spin polarization has been rarely considered. Here we report a controllable method to manipulate its electron spin polarization by tuning the concentration of Ti vacancies. The characterizations confirm the emergence of spatial spin polarization among Ti-defected TiO
, which promotes the efficiency of charge separation and surface reaction via the parallel alignment of electron spin orientation. Specifically, Ti
O
, possessing intensive spin polarization, performs 20-fold increased photocatalytic hydrogen evolution and 8-fold increased phenol photodegradation rates, compared with stoichiometric TiO
. Notably, we further observed the positive effect of external magnetic fields on photocatalytic activity of spin-polarized TiO
, attributed to the enhanced electron-spin parallel alignment. This work may create the opportunity for tailoring the spin-dependent electronic structures in metal oxides.
Hematite attracts intensive interest as an adsorbent for water purification, but the oversized dimension and inherent high‐spin Fe(III) restrict its adsorption capability and kinetics. Herein a ...spatial‐confinement strategy is reported that synthesizes ultrafine α‐Fe2O3 benefiting from nanogrids constructed by predeposition of TiO2 nanodots in the MCM‐41 channel, and that tunes the spin‐state of Fe(III) from high‐spin to low‐spin induced by the strong guest–host interaction between the ultrafine Fe2O3 with SiO2 (MCM‐41). The low‐spin Fe(III) endorses strong bonding with anionic adsorbates, and significantly facilitates the electrons transfer from Fe2O3 to SiO2 to form a highly positive charged surface, and thereby shows superior electrostatic multilayer adsorption performance to different kinds of anionic contaminations. Specifically, the maximum uptake, adsorption rate, and distribution coefficient (Kd) for Rose Bengal dye reach as high as 1810 mg g−1, 1644 g (g min)−1, and 2.2 × 106 L kg−1, which are more than 8, 230, and 3700 times higher than those of commercial activated carbon, respectively. It also shows outstanding purification performance for real field water. It is demonstrated that a strong guest–host interaction can alter the spin‐state of transition metal oxides, which may pave a new way to improve their performance in adsorption and other applications like catalysis.
Spin‐transition of hematite is realized via strong interaction between ultrafine α‐Fe2O3 and SiO2. The spatial confinement strategy allows uniform deposition of ultrafine α‐Fe2O3 on mesoporous MCM‐41, which produces low‐spin α‐Fe2O3 with stronger bonding strength with adsorbates, constructs a highly positive charged surface, and thus affords fast and deep adsorption ability for water purification and other appealing application prospects.
Polymers shape human life but they also have been identified as pollutants in the oceans due to their long lifetime and low degradability. Recently, various researchers have studied the impact of ...(micro)plastics on marine life, biodiversity, and potential toxicity. Even if the consequences are still heavily discussed, prevention of unnecessary waste is desired. Especially, newly designed polymers that degrade in seawater are discussed as potential alternatives to commodity polymers in certain applications. Biodegradable polymers that degrade in vivo (used for biomedical applications) or during composting often exhibit too slow degradation rates in seawater. To date, no comprehensive summary for the degradation performance of polymers in seawater has been reported, nor are the studies for seawater‐degradation following uniform standards. This review summarizes concepts, mechanisms, and other factors affecting the degradation process in seawater of several biodegradable polymers or polymer blends. As most of such materials cannot degrade or degrade too slowly, strategies and innovative routes for the preparation of seawater‐degradable polymers with rapid degradation in natural environments are reviewed. It is believed that this selection will help to further understand and drive the development of seawater‐degradable polymers.
Plastic pollution of the oceans is a major concern today due to the long life of commodity polymers. The degradation profiles of conventional biodegradable polymers, such as polylactide, polycaprolactone, and others in seawater, are reviewed. As many of them degrade relatively slowly, additional strategies for the development of seawater‐degradable polymers are highlighted.
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