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Three-dimensional (3D) porous graphene materials with few layer nature and non-stacked structural feature afford significant advantages in high electrical conductivity, large surface area, and interconnected porous nanostructures. However, the structure evolution of porous graphene under high temperature is poorly understood. In this contribution, 3D double-layer templated graphene (DTG) composed of two non-stacked graphene layers with interlayer spacing around 15 nm and separated by a large quantity of protuberances, was employed as a special case to track the structure evolution of 3D porous graphene at high temperature. Compared with thermally reduced graphene oxide with easy graphitized nature, the unique non-stacked DTG structure was well preserved after a high-temperature annealing at 1600 °C. With limited self-healing of defects for graphene layers, and with preservation of mesosized protuberances that prevent graphene layers stacking during annealing, DTG is regarded as ‘hard carbon’ (‘non-graphitizable carbon’). The electron microscopy, Raman spectroscopy, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, gravimetric elemental analysis, nitrogen/water physisorption, and probe reactions of electrochemical oxygen reduction reaction were employed to reveal the graphitization degree and surface chemistry of non-stacked DTG after high-temperature treatment.

A bifunctional graphene catalyst with abundant topological defects is achieved via the carbonization of natural gelatinized sticky rice to probe the underlying oxygen electrocatalytic mechanism. A nitrogen-free configuration with adjacent pentagon and heptagon carbon rings is revealed to exhibit the lowest overpotential for both oxygen reduction and evolution catalysis. The versatile synthetic strategy and novel insights on the activity origin facilitate the development of advanced metal-free carbocatalysts for a wide range of electrocatalytic applications.

Fenton oxidation using an aqueous mixture of Fe(2+) and H2 O2 is a promising environmental remediation strategy. However, the difficulty of storage and shipment of concentrated H2 O2 and the generation of iron sludge limit its broad application. Therefore, highly efficient and cost-effective electrocatalysts are in great need. Herein, a graphene catalyst is proposed for the electro-Fenton process, in which H2 O2 is generated in situ by the two-electron reduction of the dissolved O2 on the cathode and then decomposes to generate (.) OH in acidic solution with Fe(2+) . The π bond of the oxygen is broken whereas the σ bond is generally preserved on the metal-free reduced graphene oxide owing to the high free energy change. Consequently, the oxygen is reduced to H2 O2 through a two-electron pathway. The thermally reduced graphene with a high specific surface area (308.8 m(2) g(-1) ) and a large oxygen content (10.3 at %) exhibits excellent reactivity for the two-electron oxygen reduction reaction to H2 O2 . A highly efficient peroxide yield (64.2 %) and a remarkable decolorization of methylene blue (12 mg L(-1) ) of over 97 % in 160 min are obtained. The degradation of methylene blue with hydroxyl radicals generated in situ is described by a pseudo first-order kinetics model. This provides a proof-of-concept of an environmentally friendly electro-Fenton process using graphene for the oxygen reduction reaction in an acidic solution to generate H2 O2 .

The oxygen evolution reaction (OER) has attracted tremendous explorations in both fundamental and application fields recently, due to its core status in next-generation energy conversion and storage technologies, such as water splitting and metal-air batteries. Transition metal-based compounds, especially the NiFe layered double hydroxides (NiFe LDHs) have been well-established as the most effective and cost-efficient electrocatalysts to boost the sluggish water oxidation and improve the energy efficiency. Nevertheless, a favorable substrate is highly required to expose the poorly conductive active phases and enhance reactivities of OER. In this review, the recent advances concerning synthetic strategies, hierarchical structures, and OER performances of NiFe LDH/nanocarbon hybrid electrocatalysts are summarized. A brief description of OER catalysis, LDHs, and nanocarbon materials is presented firstly, followed by a thorough overview of various investigations according to their synthetic methods and structural characters. The development of high-performance OER catalysts is covered by both a short summary and a presentation of future prospects. This review provides stimulatory knowledge and sheds fresh light into the development of advanced functional materials with a wise hybridization of active phases and conductive substrates.

Efficient oxygen and hydrogen evolution electrocatalysts, based on low-cost and earth-abundant elements, are strongly required for sustainable hydrogen production through water splitting. Herein, we fabricated a monolithic-structured electrode by facilely electrodepositing NiCoFe ternary layered double hydroxides (LDHs) onto 3D conductive scaffolds, providing abundant fully exposed active sites for electrochemical reactions. The moderate Co dopant effectively improved the electrical conductivity of the LDH phase and substantially increased its intrinsic activity. When used for oxygen evolution, the as-obtained monolith LDH electrode exhibited superior kinetics with 275 mV overpotential required to achieve 10 mA cm−2 in 0.10 M KOH, as well as a very low activation energy of 21.0 kJ mol−1. Such a freestanding electrode was also able to catalyze hydrogen evolution efficiently in alkaline media, which further enabled a high-efficiency water electrolyzer delivering 10 mA cm−2 at a very low cell voltage of 1.62 V in 1.0 M KOH. This sheds fresh insight into the principle and process of practical water electrolysis through the rational design of precious-metal-free bifunctional electrodes with a monolithic configuration.

Both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) hold the core position in various sustainable energy systems. Attributed to their sluggish kinetics, the principle and concept to achieve efficient electrocatalysts for a sustainable catalytic process, especially bi-functional electrocatalysts with abundant active centers and 3D conductive scaffolds for both OER and ORR, are strongly considered. In this contribution, rather than physically mixing active catalyst flakes with conductive fillers, a hybrid electrocatalyst with ‘active point–conductive line–active point’ connections was proposed and validated. As a proof-of-concept, Co-based active sites embedded on layered double oxide (LDO) substrates interlinked with carbon nanotubes (CNTs) were realized and exhibited a superior bi-functional activity for both OER and ORR in an alkaline electrolyte. The LDO/CNT hybrids catalyzed the OER to reach 10.0 mA cm−2 at 1.64 V vs. RHE, and the ORR to reach 3.0 mA cm−2 at 0.65 V vs. RHE, with a potential gap of 0.99 V. Such model catalysts of LDO/CNT hybrids even delivered a better bi-functional performance than routine noble metal catalysts (e.g. Pt/C and IrO2). The novel strategy of combining metal compounds and carbon nanomaterials through ‘point–line–point’ configurations can be applied to other hierarchical composites with multi-building blocks, aiming at promising applications in energy storage and environmental protection.

Multi-metallic (oxy)hydroxide materials are some of the most promising alternatives for superb water oxidation electrocatalysts. Herein, a series of graphene/NiFe (oxy)hydroxides were fabricated to investigate the role of the Fe/Ni ratio in regard to the resultant physical structures, decoration styles, and combined catalytic activities. With the Fe content increasing, a phase evolution from Fe doped Ni(OH)2/NiO(OH) to Ni doped FeO(OH) was demonstrated. The moderate guest-metal substitution into the host-oxyhydroxide framework (Fe into Ni or Ni into Fe) substantially enhanced the oxygen evolution activity with a decrease in both the Tafel slope and overpotential. In addition, the NiO(OH) and FeO(OH) frameworks exhibited distinct properties and performances for the oxygen evolution reaction due to the different metal–oxygen bond lengths and adsorption energies of the intermediates.

Structural hierarchy plays an important role in the biological world and for functional materials with optimized properties and high efficiency. As promising candidates for various energy storage systems, hierarchical porous carbon/graphene materials have been intensively investigated over the past decades, while the favorable regulation of their hierarchical porosity remains a challenge. Herein, porous CaO serves as both the catalyst and template for a versatile chemical vapor deposition (CVD) of hierarchical porous graphene. The gas atmosphere during CVD and nanostructure of adopted catalysts impact significantly on the graphitization degree and hierarchical porosity of resultant materials. The as-fabricated material exhibits abundant microsized in-plane vacancies, mesosized wrinkled pores, and macrosized strutted cavities, thereby contributing to a strong surface entrapment, short ion diffusion pathways, rapid mass transport, low interfacial resistance, and robust framework. It is demonstrated as a favorable scaffold for lithium–sulfur battery cathodes with superior rate capability, high coulombic efficiency, and excellent stability. A high capacity of 357 (656 ) is manifested at the current rate of 5.0 C, exhibiting a 74% retention of the capacity at 0.1 C. The first use of CaO-templated CVD growth of graphene reported herein opens up new perspectives on the effective fabrication of hierarchical porous graphene materials on metal oxide catalysts with promising applications in energy storage, catalysis, adsorption, drug delivery, and so on.

A cost-effective and highly efficient oxygen evolution reaction (OER) electrocatalyst will be significant for the future energy scenario. The emergence of the core-shell heterostructure has invoked new feasibilities to inspire the full potential of non-precious-metal candidates. The shells always have a large thickness, affording robust mechanical properties under harsh reaction conditions, which limits the full exposure of active sites with highly intrinsic reactivity and extrinsic physicochemical characters for optimal performance. Herein, a nanosized CoNi hydroxide@hydroxysulfide core-shell heterostructure is fabricated via an ethanol-modified surface sulfurization method. Such a synthetic strategy is demonstrated to be effective in controllably fabricating a core-shell heterostructure with an ultrathin shell (4 nm) and favorable exposure of active sites, resulting in a moderately regulated electronic structure, remarkably facilitated charge transfer, fully exposed active sites, and a strongly coupled heterointerface for energy electrocatalysis. Consequently, the as-obtained hydroxide@hydroxysulfide core-shell is revealed as a superior OER catalyst, with a small overpotential of 274.0 mV required for 10.0 mA cm-2 , a low Tafel slope of 45.0 mV dec-1 , and a favorable long-term stability in 0.10 M KOH. This work affords fresh concepts and strategies for the design and fabrication of advanced core-shell heterostructures, and thus opens up new avenues for the targeted development of high-performance energy materials.

Oxygen evolution reaction (OER) is one of the research focuses in clean energy field, for it is the core reaction in electrochemical water splitting, rechargeable metal-air batteries, etc. With a complicated four-electron process, OER suffers from its slow reaction rate. Therefore, the exploration of efficient OER electrocatalysts has become a significant topic in the research of advanced energy materials. Transition metal compounds exhibit great potential towards highly active OER electrocatalysts, and rational regulations have been applied to boost their OER performances. Among these strategies, anion regulation is an emerging but effective way to improve the OER activity of transition metal compounds. In this review, the recent advances in the anion regulated multi-anion transition metal compounds as OER catalysts are introduced, concerning about the synthesis methods, the regulation of the anions and its effect on the OER activity. The anion regulation during the OER test, i.e. the surface oxidation of the catalysts, is also discussed in this review. Then the researches are introduced according to the type of the regulated anions. This review is expected to inspire more insights into the composition and structure regulation of OER catalysts, and further researches on transition metal-based energy materials.

Various gas-involving energy electrocatalysis, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER), has witnessed increasing concerns recently for the sake of clean, renewable, and efficient energy technologies. However, these heterogeneous reactions exhibit sluggish kinetics due to multistep electron transfer and only occur at triple-phase boundary regions. Up to now, tremendous attention has been attracted to develop cost-effective and high-performance electrocatalysts to boost the electrocatalytic activities as promising alternatives to noble metal counterparts. In addition to the prolific achievements in materials science, the advances in interface chemistry are also very critical in consideration of the complex phenomena proceeded at triple-phase boundary regions, such as mass diffusion, electron transfer, and surface reaction. Therefore, insightful principles and effective strategies for a comprehensive optimization, ranging from active sites to electrochemical interface, are necessary to fully enhance the electrocatalytic performance aiming at practical device applications. In this Account, we give an overview of our recent attempts toward efficient gas-involving electrocatalysis with multiscale principles from the respect of electronic structure, hierarchical morphology, and electrode interface step by step. It is widely accepted that the intrinsic activity of individual active sites is directly influenced by their electronic structure. Heteroatom doping and topological defects are demonstrated to be the most effective strategies for metal-free nanocarbon materials, while the cationic (e.g., Ni, Fe, Co, Sn) and anionic (e.g., O, S, OH) regulation is revealed to be a promising method for transition metal compounds, to alter the electronic structure and generate high activity. Additionally, the apparent activity of the whole electrocatalyst is significantly impacted by its hierarchical morphology. The active sites of nanocarbon materials are expected to be enriched on the surface for a full exposure and utilization; the hybridization of other active components with nanocarbon materials should achieve a uniform dispersion in nanoscale and a strongly coupled interface, thereby ensuring the electron transfer and boosting the activity. Furthermore, steady and favorable electrochemical interfaces are strongly anticipated in working electrodes for optimal reaction conditions. The powdery electrocatalysts are suggested to be constructed into self-supported electrodes for more efficient and stable catalysis integrally, while the local microenvironment can be versatilely modified by ionic liquids with more beneficial gas solubility and hydrophobicity. Collectively, with the all-round regulation of the electronic structure, hierarchical morphology, and electrode interface, the electrocatalytic performances are demonstrated to be comprehensively facilitated. Such multiscale principles stemmed from the in-depth insights on the structure-activity relationship and heterogeneous reaction characteristics will no doubt pave the way for the future development of gas-involving energy electrocatalysis, and also afford constructive inspirations in a broad range of research including CO

N-doped herringbone carbon nanofibers (N-HBCNFs) were efficiently fabricated by chemical vapor deposition on Ni nanoparticles derived from layered double hydroxide precursors. The as-obtained CNFs were with an average diameter of ∼60 nm, a high purity of ∼91.6%, and a large specific surface area of 108.1 m 2 g −1 . When employed as anode materials, the N-HBCNFs yielded a reversible capacity of 500.0 mAh g −1 at a current density of 0.10 C (1.0 C = 372 mA g −1 ) and rapid lithium storage properties with a high capacity of 141.6 mAh g −1 at 5.0 C. When the N-HBCNFs were used as catalyst for oxygen reduction reaction, an onset potential of 0.85 V, an electron transfer number of 3.1, and a current retention of 69.1% after 16,000 s test were detected, indicating the good reactivity of N-HBCNF catalyst for electrocatalysis application. The superior performance of N-HBCNFs was attributed to their enlarged graphitic lattice spacings and abundant edges on the surface, which afforded more active sites for both Li ion storage and oxygen reduction reaction. Thus, the N-HBCNFs are promising nanocarbon materials for various applications in lithium ion batteries, lithium-sulfur batteries, lithium-air batteries, fuel cells, and so on.

The oxygen evolution reaction (OER) is extensively involved in various sustainable energy processes and systems, such as water splitting, fuel cells, and metal–air batteries. Towards superior OER performance, the wise integration of transition metal compounds with nanocarbon materials is a promising strategy. Herein, a mildly oxidized graphene/single-walled carbon nanotube hybrid was introduced to regulate and control the hybridization of nickel–iron layered double hydroxides into a nanocarbon scaffold. The oxygen functionalities and defects anchored the nucleation and in situ growth of dual-sized layered double hydroxides, leading to a hierarchical porous structure for smooth mass diffusion, intimate interfaces for rapid charge transfer, and efficiently utilized active sites. Attributed to the synergy of individual components and the unique structural features, the as-fabricated composites exhibited superior OER performance with a small onset overpotential (ca. 240 mV), a low overpotential required for 10 mA cm−2 (ca. 350 mV), and a decreased Tafel slope (ca. 54 mV dec−1) in 0.10 M KOH. This work provides a brilliant catalyst for water oxidation and more importantly, opens up new avenues for preparing nanocarbon-based multi-functional composites applicable in heterogeneous catalysis, energy conversion and storage, and so on.

The oxygen evolution reaction (OER) plays a key role in various sustainable energy systems, such as solar cells, fuel cells and metal–air batteries. The wise integration of transition metal compounds with macroscale current collectors is a promising strategy to achieve OER catalysts with high utilization efficiency. Herein, graphene with superior electron pathways, high surface area, excellent conductive and mechanical properties, and conjugate planes to anchor other phases with good dispersion was employed as the barrier between 3D Ni foam and NiFe-LDHs for 3D monolith electrodes. The as-obtained electrode exhibited a remarkably low onset overpotential of 240 mV, a small overpotential of 325 mV for 10 mA cm−2 and a substantially decreased Tafel slope of 44 mV dec−1 in 0.1 M KOH. The graphene barrier herein not only provides a novel hydrophobic substrate to modulate the growth of 3D NiFe-LDHs with good dispersion, but also delivers a strongly coupled interface between the active phase and current collectors. Consequently, the as-obtained graphene mediated 3D monolith electrode exhibited a very high electrochemically active surface area, an optimal interfacial junction, as well as superior OER performance. This work provides a novel catalyst for OER and more importantly, it reveals the role of graphene in modulating the interfacial features of various composites, which is general and can be employed in many material systems for satisfactory applications in heterogeneous catalysis, energy conversion and storage, sensors and so on.

Graphene is inclined to stack with each other that greatly hinders the full utilization of its intrinsic extraordinary properties. Introducing protuberant spacers is a straightforward strategy to avoid the stacking of graphene nanosheets, resulting in a novel unstacked double-layer templated graphene (DTG) structure. Herein, a family of layered double hydroxides were used for the bulk chemical vapor deposition (CVD) of DTG in a fluidized-bed reactor. A high specific surface area of 1554.2 m2 g−1 and a large pore volume of 1.70 cm3 g−1 were achieved. When used as the electrode material for supercapacitors, the DTG afforded a specific capacitance of 65.5 F g−1 at a sweep rate of 5.0 mV s−1 and a capacitance retention of 77% when the sweep rate was increased to 500 mV s−1. Therefore, the DTG obtained via fluidized bed CVD is a promising electrode material for supercapacitor applications. © 2014 American Institute of Chemical Engineers AIChE J, 61: 747–755, 2015

The emergence of van der Waals (vdW) heterostructures of 2D materials has opened new avenues for fundamental scientific research and technological applications. However, the current concepts and strategies of material engineering lack feasibilities to comprehensively regulate the as-obtained extrinsic physicochemical characters together with intrinsic properties and activities for optimal performances. A 3D mesoporous vdW heterostructure of graphene and nitrogen-doped MoS2 via a two-step sequential chemical vapor deposition method is constructed. Such strategy is demonstrated to offer an all-round engineering of 2D materials including the morphology, edge, defect, interface, and electronic structure, thereby leading to robustly modified properties and greatly enhanced electrochemical activities. The hydrogen evolution is substantially accelerated on MoS2 , while the oxygen reduction and evolution are significantly improved on graphene. This work provides a powerful overall engineering strategy of 2D materials for electrocatalysis, which is also enlightening for other nanomaterials and energy-related applications.

Rechargeable flexible solid Zn-air battery, with a high theoretical energy density of 1086 Wh kg

Bifunctional electrocatalysis for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) constitutes the bottleneck of various sustainable energy devices and systems like rechargeable metal–air batteries. Emerging catalyst materials are strongly requested toward superior electrocatalytic activities and practical applications. In this study, transition metal hydroxysulfides are presented as bifunctional OER/ORR electrocatalysts for Zn–air batteries. By simply immersing Co-based hydroxide precursor into solution with high-concentration S2−, transition metal hydroxides convert to hydroxysulfides with excellent morphology preservation at room temperature. The as-obtained Co-based metal hydroxysulfides are with high intrinsic reactivity and electrical conductivity. The electron structure of the active sites is adjusted by anion modulation. The potential for 10 mA cm−2 OER current density is 1.588 V versus reversible hydrogen electrode (RHE), and the ORR half-wave potential is 0.721 V versus RHE, with a potential gap of 0.867 V for bifunctional oxygen electrocatalysis. The Co3FeS1.5(OH)6 hydroxysulfides are employed in the air electrode for a rechargeable Zn–air battery with a small overpotential of 0.86 V at 20.0 mA cm−2, a high specific capacity of 898 mAh g−1, and a long cycling life, which is much better than Pt and Ir-based electrocatalyst in Zn–air batteries.

Water oxidation represents the core process of many sustainable energy systems, such as fuel cells, rechargeable metal-air batteries, and water splitting. Material surface defects with high-energy hanging bonds possess superb intrinsic reactivity, whose actual performance is limited by the dimension and conductivity of the electrocatalyst. Herein we propose a surface defect-rich perovskite electrocatalyst through a p-block metal regulation concept to achieve high performance for oxygen evolution. As a typical p-metal, Sn4+ dissolves from the solid phase from model SnNiFe perovskite nanodots, resulting in abundant surface defects with superior water oxidation performance. An oxygen pool model and a fusion-evolution mechanism are therefore proposed for the in-depth understanding of p-block metal regulation and the oxygen evolution reaction. The energy chemistry unveiled herein provides insights into water oxidation and helps to tackle critical issues in multi-electron oxygen electrocatalysis., Electrocatalysts that possess high densities of surface defects show great promise for efficient water oxidation. Here the authors demonstrate that regulating the p-block metal content in perovskite nanodots imparts these materials with abundant surface defects and excellent electrocatalytic activity.

Microbial fuel cells (MFCs) can convert organics in wastewater directly to electricity, and improving oxygen reduction reaction (ORR) performance is critical to their development and future applications. Electrocatalytic ORR performance is determined by the intrinsic activity and accessible amounts of active sites. A surface nitrogen-enriched carbon coaxial nanocable (NCCN) is applied as an ORR electrocatalyst and combined with activated carbon (AC) with 80 wt% addition as a carbon-carbon composite air cathode in MFCs. The fully exposed nitrogen active sites of NCCN contribute to the enhanced ORR activity, while the graphitized core affords a rapid pathway for electron transportation. AC serves as a spacer to construct a porous framework with interconnected ion diffusion channels. This cathode thus exhibits a maximum power density of 2090 mW m-2 , 120% higher than commercial Pt/C electrocatalysts, and also 6% higher than the pure NCCN, indicating a synergistic effect between NCCN and AC. A high-performance NCCN-AC air cathode with a great promise for future MFC applications is reported and an effective strategy to bridge the electrocatalytic performance from nanomaterials to practical devices is presented.

Objectives To investigate the role of hypoxia in vasculogenic mimicry (VM) of salivary adenoid cystic carcinoma (SACC) and the underlying mechanism involved. Materials and methods Firstly, wound healing, transwell invasion, immunofluorescence and tube formation assays were performed to measure the effect of hypoxia on migration, invasion, EMT and VM of SACC cells, respectively. Then, immunofluorescence and RT‐PCR were used to detect the effect of hypoxia on VE‐cadherin and VEGFA expression. And pro‐vasculogenic mimicry effect of VEGFA was investigated by confocal laser scanning microscopy and Western blot. Moreover, the levels of E‐cadherin, N‐cadherin, Vimentin, CD44 and ALDH1 were determined by Western blot and immunofluorescence in SACC cells treated by exogenous VEGFA or bevacizumab. Finally, CD31/ PAS staining was performed to observe VM and immunohistochemistry was used to determine the levels of VEGFA and HIF‐1α in 95 SACC patients. The relationships between VM and clinicopathological variables, VEGFA or HIF‐1α level were analysed. Results Hypoxia promoted cell migration, invasion, EMT and VM formation, and enhanced VE‐cadherin and VEGFA expression in SACC cells. Further, exogenous VEGFA markedly increased the levels of N‐cadherin, Vimentin, CD44 and ALDH1, and inhibited the expression of E‐cadherin, while the VEGFA inhibitor reversed these changes. In addition, VM channels existed in 25 of 95 SACC samples, and there was a strong positive correlation between VM and clinic stage, distant metastases, VEGFA and HIF‐1α expression. Conclusions VEGFA played an important role in hypoxia‐induced VM through regulating EMT and stemness, which may eventually fuel the migration and invasion of SACC.

Aqueous preoxidation strategy for in situ hybridization of oxidative perovskite and reductive conductive frameworks., Perovskite oxides with poor conductivity call for three-dimensional (3D) conductive scaffolds to demonstrate their superb reactivities for oxygen evolution reaction (OER). However, perovskite formation usually requires high-temperature annealing at 600° to 900°C in air, under which most of the used conductive frameworks (for example, carbon and metal current collectors) are reductive and cannot survive. We propose a preoxidization coupled electrodeposition strategy in which Co2+ is preoxidized to Co3+ through cobalt Fenton reaction in aqueous solution, whereas the reductive nickel framework is well maintained during the sequential annealing under nonoxidative atmosphere. The in situ–generated Co3+ is inherited into oxidized perovskites deposited on 3D nickel foam, rendering the monolithic perovskite electrocatalysts with extraordinary OER performance with an ultralow overpotential of 350 mV required for 10 mA cm−2, a very small Tafel slope of 59 mV dec−1, and superb stability in 0.10 M KOH. Therefore, we inaugurate a unique strategy for in situ hybridization of oxidative active phase with reductive framework, affording superb reactivity of perovskite electrocatalyst for efficient water oxidation.

Three-dimensional hierarchical porous graphene materials with unique properties are of significant importance for the exploration of advanced electrocatalysts for both the oxygen reduction and evolution reactions (ORR/OER). Templated chemical vapor deposition is a favorable strategy to fabricate this kind of graphene, but the number of effective templates is limited. Here, silicoaluminophosphate (SAPO-34) zeolite crystals were used as the catalytic templates for the deposition of hierarchical porous graphene. The graphene obtained consisted of micron-size hollow cubes with mesoporous/nanoporous facets, and ultrathin walls, precisely replicating the structure of the cube-like SAPO-34 zeolite particles. A high doping level of nitrogen (6.84 at%) was achieved by subsequent annealing at 700 °C under ammonia before template removal. Because of the unique porosity, abundant defects, and favorable N-doping, the N-doped graphene exhibited considerable reactivity for both ORR and OER.

Nanometer-sized hydroxide active centers are uniformly and strongly hybridized into a graphene framework by means of defect-anchored nucleation and spatially confined growth, resulting in a superior electrocatalyst for oxygen evolution reaction. This family of strongly coupled complexes and the topology-assisted fabrication strategy is expected to open up new avenues of research. It sheds light on a novel branch of advanced nano-architectured materials.

Rechargeable flexible solid Zn-air battery, with a high theoretical energy density of 1086 Wh kg−1, is among the most attractive energy technologies for future flexible and wearable electronics; nevertheless, the practical application is greatly hindered by the sluggish oxygen reduction reaction/oxygen evolution reaction (ORR/OER) kinetics on the air electrode. Precious metal-free functionalized carbon materials are widely demonstrated as the most promising candidates, while it still lacks effective synthetic methodology to controllably synthesize carbocatalysts with targeted active sites. This work demonstrates the direct utilization of the intrinsic structural defects in nanocarbon to generate atomically dispersed Co–Nx–C active sites via defect engineering. As-fabricated Co/N/O tri-doped graphene catalysts with highly active sites and hierarchical porous scaffolds exhibit superior ORR/OER bifunctional activities and impressive applications in rechargeable Zn-air batteries. Specifically, when integrated into a rechargeable and flexible solid Zn-air battery, a high open-circuit voltage of 1.44 V, a stable discharge voltage of 1.19 V, and a high energy efficiency of 63% at 1.0 mA cm−2 are achieved even under bending. The defect engineering strategy provides a new concept and effective methodology for the full utilization of nanocarbon materials with various structural features and further development of advanced energy materials.

A hydroxide/graphene hybrid electrocatalyst for oxygen evolution reaction is proposed by Q. Zhang and co-workers, as described on page 4516. Nanosized hydroxide active centers are uniformly and strongly hybridized into a nitrogen-doped graphene framework via defect-anchored nucleation and spatially confined growth. The as-obtained hydroxide/graphene is demonstrated to overperform commercial Ir/C catalysts and compete favorably against reported alternatives for high-performance oxygen evolution reactivity.