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As low-cost electrocatalysts for oxygen reduction reaction applied to fuel cells and metal-air batteries, atomic-dispersed transition metal-nitrogen-carbon materials are emerging, but the genuine mechanism thereof is still arguable. Herein, by rational design and synthesis of dual-metal atomically dispersed Fe,Mn/N-C catalyst as model object, we unravel that the O2 reduction preferentially takes place on FeIII in the FeN4/C system with intermediate spin state which possesses one eg electron (t2g4eg1) readily penetrating the antibonding π-orbital of oxygen (Figure 1).[1,2] Both magnetic measurements and theoretical calculation reveal that the adjacent atomically dispersed Mn-N moieties can effectively activate the FeIII sites by both spin-state transition and electronic modulation, rendering the excellent ORR performances of Fe,Mn/N-C in both alkaline and acidic media (halfwave positionals are 0.928 V in 0.1 M KOH, and 0.804 V in 0.1 M HClO4), and good durability, which outperforms and has almost the same activity of commercial Pt/C, respectively. In addition, it presents a superior power density of 160.8 mW cm−2 and long-term durability in reversible zinc–air batteries. We believe our work will brings new insight into the oxygen reduction reaction process on the metal-nitrogen-carbon active sites, undoubtedly leading the exploration towards high effective low-cost non-precious catalysts.

MATERIALS FOR HUMANITY (MH 21)

Carbon-Based Electrocatalyst: Synthetic Strategies and Chemical Environmental Regulations

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MH 21 is arranged around 6 themes that focus attention on pressing needs that should be addressed to enhance the well-being of communities and provide a forum for presenting breakthrough discoveries.

technical paper

Development and implementation of novel and energy-efficient technologies to mitigate greenhouse gas emissions in the atmosphere, particularly CO2, is a vital step towards fossil fuel-based sustainable energy. Removal of greenhouse gases from dilute emissions has been identified as one of the seven chemical separations to change the world. Additionally, the requirement for long-duration human task performance in confined spaces such as submarines, spacecraft or underground citadels has made the removal of low-concentration CO2 (< 0.5%) a critical technology. Reducing energy consumption is another promising way to reduce CO2 emissions. The energy use for separation and purification processes accounts for 40 % of the total energy use in chemical industry. Especially, high-purity ethylene (C2H4) and propylene (C3H6), two most produced chemicals, inevitably contain low concentrations of acetylene (C2H2) and propyne (C3H4) during the production. Catalytic hydrogenation and solvent absorption are two main processes for alkynes removal but with high energy consumption and low removal rate. Thus, tremendous energy savings are expected by applying advanced adsorptive separation technologies based on porous materials. The key feature of these environmentally friendly, energy-efficient separation technologies is the porous adsorbent or porous media. Hybrid ultramicroporous materials (HUMs) with electronegative anion pillars lined up within the pore channels have been illustrated as promising adsorbents for gas separation and CO2 capture. Herein, HUMs with fine-tuned pore dimensions are synthesized via mechano-assisted method and used for efficient low-concentration carbon capture and alkynes removal from olefins via strong host-guest and guest-guest interactions.

Hybrid Ultramicroporous Materials for low-concentration carbon capture and alkyne removal from olefines

Green and bio-waste represents more than 44% of urban municipal waste. Here, we explore the valorization of this waste by transforming it into composites using fungi. Indeed, fungi grow by degrading the lignocellulosic content of waste and by developing a highly interconnected network called mycelium. This mycelium is composed of chitin, cellulose, and protein, and bind the non-degraded components together. In this work, we investigate the incidence of food sources on the growth of the mycelium of two commonly used fungi, the Lingzi mushroom and the Grey Oyster mushroom. We find that foods are natural catalysts of the growth. Furthermore, we develop mixtures, or inks that can be used to 3D print such materials using an extrusion method. The composites formed from waste and mycelium are interesting for their insulation properties, mechanics, decorative, etc.

Growing mycelium-bound composite using agricultural waste

Reducing landfill waste by 30% and increasing solar energy deployment to 2 GWp (giga-watt peak) are two of the key targets in the Singapore Green Plan 2030. While seemingly mutually-exclusive, increasing solar energy deployment, if not planned and handled properly, will eventually lead to increasing landfill waste. In fact, due to the relatively long useful lifetime (>10 years) of solar cells, it was not until recently that wastes from solar cells starts to be of concerns. It was estimated that by 2030, waste from solar panels alone will reach millions of tons. On the contrary, the current recycling technologies for solar waste is still rudimentary - only precious metals such as silver and copper are economical to be recycled. This presents both environmental and economical problems because the bulk of solar cells which are made of silicon are not recycled. In this work, we recycled Silicon from solar cells into thermoelectrics. Leveraging on our expertise in thermoelectrics, we fine tuned and optimized the carrier concentration using phosphorus, and engineered low thermal conductivity via germanium doping. ZT as high as 0.4 is achieved at 800 K, which is one of the highest in silicon. Our work opens a pathway for recycling semiconductor waste into high performance functional materials for power generation and cooling applications.

Upcycling of Photovoltaics Silicon into Thermoelectrics by Turning Minority into Majority Carrier

Artificial intelligence and machine learning (AI/ML) approaches for material design combined with 3D printing are capable of harnessing the bio-inspired design paradigm, creating de novo structures with extraordinary properties from basic building blocks. To valorize biomass such as food waste, biomass waste from industrial processes, or algae, we use bottom-up processes to convert biomass first into 3D printable materials, reducing need for plastic waste generation, then into advanced, functional materials including architected hierarchical composites, all using a conversion of materials into wave- and sound-based models.

Additive manufacturing of biomass-derived renewable composites with AI accelerated bottom-up design

All-solid-state sodium batteries employing fast ion-conducting sulfides, show great promise for safe, low-cost energy storage systems for large-scale applications. Among the candidate systems, Na3SbS4 (NAS) is particularly promising by being both highly ionic conductive and compatible with humid air while other common sulfide electrolytes suffer a lot from decomposing in ambient environment. The combination of fast Na+ ion migration and low-cost processability significantly benefits the large-scale application and industrialization.
Considering that partial substitution of sulfur by halide ions can induce more mobile sodium vacancies in NAS and potentially improve the interfacial stability towards sodium metal anode, here we explored a low-cost structural modification to NAS by aqueous synthesis to enhance both the rate capability and the cycle life of solid-state batteries based on this optimized solid electrolyte. To this end halide doped NAS electrolytes are synthesized from aqueous solution. Here we focus on the effect of Bromide doping of NAS on its ionic conductivity and kinetic electrochemical stability. It is observed that Br-doped NAS exhibits greatly reduced activation energy. Total ionic conductivity is more than doubled from 0.13 mS/cm to 0.31 mS/cm through this low-cost halide doping approach allowing for higher critical current densities. Stable cycling profiles of the doped NAS vs both sodium-metal anodes and sodium-tin ally anodes evidenced a major enhancement of the electrochemical stability and thus a path towards longer cycle life all-solid state sodium metal batteries.


Low cost aqueous synthesis and doping of a high performance sodium solid electrolyte

Rechargeable lithium−oxygen batteries (LOBs) have attracted increasing attention due to their high energy density but highly rely on the development of efficient oxygen catalysts for reversible Li2O2 deposition/decomposition. Herein, highly porous carbon nanocubes with a specific surface area up to 1600 m2 g−1 are synthesized and utilized to tightly anchor Ru nanoparticles for using as the oxygen-cathode catalyst in LOBs, achieving a low charge/discharge potential gap of only 0.75 V, a high total discharge capacity of 17,632 mA h g−1, and a superb cycling performance of 550 cycles at 1000 mA g−1. Comprehensive ex situ and operando characterizations unravel that the outstanding LOB performance is ascribed to the highly porous catalyst structure embedding rich active sites that synergistically function in reducing overpotentials, suppressing parasitic reactions, accommodating reaction products, and promoting mass and charge transportation.

Ru-embedded Highly Porous Carbon Nanocubes Derived from Metal Organic Frameworks for Catalyzing Reversible Li2O2 Formation

Co-doped molybdenum disulfide nanosheet (denoted Co-MoS2) was designed as a cathode catalyst in a lithium-sulfur battery, and was prepared by a hydrothermal method. It was demonstrated that cobalt doping induces the transformation of MoS2 from the 2H phase to the metallic 1T phase. The consequents increase the proportion of 1T phase MoS2 (1T-MoS2) with high catalytic activity while improving the stability of the catalytic site. The introduction of Co atoms also provides abundant electrons to the basal plane of the MoS2 matrix, thus improving the conductivity of semiconductor MoS2. Consequently, a sulfur cathode with Co-MoS2 contributes to a high rate performance (943 mAh g−1 at a high rate of 2 C relative to 1220 mAh g−1 at 0.3 C) as well as long cyclic stability (an ultralow capacity fading rate of 0.029% per cycle over 1000 cycles at the high current rate of 0.2 C).

Co-doped Molybdenum Disulfide Facilitating Polysulfides Transformation in Advanced Lithium-sulfur Batteries

Hybrid capacitive deionization (HCDI) is emerging as an energy-efficient alternative for brackish water desalination with low expenditure cost and favourable ion removal effectiveness by adopting battery-type electrodes in the traditional capacitive deionization (CDI) system. Herein, an unscalable electrospinning method is introduced to contrive cathode material for HCDI system. Co3O4 and nitrogen-doped carbon nanotube decoration are formed successfully and uniformly distributed with the hollow structure of free-standing carbon nanofibers (Co3O4@CNF@CNT). The conductive “bridges” provided by the CNF matrix significantly shorten the diffusion length of Na+ and promote the electrical conductivity of the Co3O4 nanoparticles. Moreover, benefiting from the incorporation of nitrogen-doped CNTs as the “medium”, the contact between electrolyte and electrode material is improved and the electrical conductivity is further enhanced. The as-prepared Co3O4@CNF@CNT cathode shows excellent pseudocapacitive performance of 395 F g-1 at a scan rate of 1 mV s-1 and superior rate performance of 279 F g-1 at 100 mV s-1. The HCDI system delivers an outstanding salt adsorption capacity (SAC) of 58.6 mg g-1 and a highest salt adsorption rate (SAR) of 12.27 mg g-1 min-1 with a potential difference of 1.4 V, indicating the great potential of applying Co3O4@CNF@CNT in the practical HCDI system.

Hierarchical tubular Co3O4/CNT structures for Efficient Hybrid Capacitive Deionization

Li-O2 battery is one of the most desired energy storages form due to its extraordinary high energy density and the readily available oxygen source from atmosphere. However, significant challenges still line up ahead from both the anode and cathode sides before the technology can be finally deployed to benefit human life. Herein, a two-birds-one-stone tactic is implemented to fabricate high-performance and flexible Li-O2 batteries utilizing only one structural backbone composed of graphene oxide (GO) aerogel embedding hollow NiCo2O4 (NCO) microspheres for both the anode and cathode. While the composite Li anode fabricated through lithium infusion exhibits an ultrahigh capacity of 3398.4 mAh g-1 and significantly inhibited dendrite growth and volume expansion, the freestanding oxygen cathode demonstrates great capability in promoting energy efficiency by catalyzing reversible Li2O2 formation. When coupled together, the resultant Li-O2 batteries manifest a superb long-term cycling stability with highly reversible discharge/charge for more than 400 cycles, apart from the remarkable mechanical deformability demonstrated by flexible pouch cells surpassing 400 hours of steady operation. By employing a full spectrum of ex-situ and operando spectroscopic and microscopic tools, mechanistics into the remarkable Li-O2 performance is unraveled.

High‐Performance Li–O2 Batteries Based on All‐Graphene Backbone

Chromium deposition affects the performance of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) which is widely used as a cathode material for solid oxide fuel cell (SOFC). [1] However, more information is required to better understand the chromium poisoning process at the microstructural level. A SOFC stack composes of several components: cathode, electrolyte, anode, and Crcontaining steels or alloys as an interconnect (Fig. 1). Chromium evaporates from steels and is transported with are stream to a cathode where it deposits, which affects the electrochemical performance of the SOFC (Fig. 2).

Carbon-Based Electrocatalyst: Synthetic Strategies and Chemical Environmental Regulations

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