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A lithium-air battery based on lithium oxide (Li 2 O) formation can theoretically deliver an energy density that is comparable to that of gasoline. Lithium oxide formation involves a four-electron reaction that is more difficult to achieve than the one- and two-electron reaction processes that result in lithium superoxide (LiO 2 ) and lithium peroxide (Li 2 O 2 ), respectively. By using a composite polymer electrolyte based on Li 10 GeP 2 S 12 nanoparticles embedded in a modified polyethylene oxide polymer matrix, we found that Li 2 O is the main product in a room temperature solid-state lithium-air battery. The battery is rechargeable for 1000 cycles with a low polarization gap and can operate at high rates. The four-electron reaction is enabled by a mixed ion–electron-conducting discharge product and its interface with air.

An overarching challenge of the electrochemical carbon dioxide reduction reaction (eCO2RR) is finding an earth-abundant, highly active catalyst that selectively produces hydrocarbons at relatively low overpotentials. Here, we report the eCO2RR performance of two-dimensional transition metal carbide class of materials. Our results indicate a maximum methane (CH4) current density of −421.63 mA/cm2 and a CH4 faradic efficiency of 82.7% ± 2% for di-tungsten carbide (W2C) nanoflakes in a hybrid electrolyte of 3 M potassium hydroxide and 2 M choline-chloride. Powered by a triple junction photovoltaic cell, we demonstrate a flow electrolyzer that uses humidified CO2 to produce CH4 in a 700-h process under one sun illumination with a CO2RR energy efficiency of about 62.3% and a solar-to-fuel efficiency of 20.7%. Density functional theory calculations reveal that dissociation of water, chemisorption of CO2 and cleavage of the C-O bond—the most energy consuming elementary steps in other catalysts such as copper—become nearly spontaneous at the W2C surface. This results in instantaneous formation of adsorbed CO—an important reaction intermediate—and an unlimited source of protons near the tungsten surface sites that are the main reasons for the observed superior activity, selectivity, and small potential., It is of high interests to develop new catalysts for selective CO2 electroreduction. Here the authors investigate two-dimensional transition metal carbides for CO2 to methane conversion with superior activity, selectivity and low overpotentials.

Solar conversion of carbon dioxide (CO2) into hydrocarbon fuels offers a promising approach to fulfill the world’s ever-increasing energy demands in a sustainable way. However, a highly active cata...

Electrical energy storage and conversion is vital to a clean, sustainable, and secure energy future. Among all electrochemical energy storage devices, lithium-air (Li-air) battery is known to offers as high as 5X greater energy density than lithium-ion batteries, representing its promise for electrical vehicles and stationery (micro-grids) applications. However, their practical realization is hindered by their poor rechargeability and rate capability, mostly due to unsuitable design of cell components, i.e., anode, cathode, and the liquid electrolyte. Here, we are presenting an aprotic Li-air battery cell, enabled by rational design of cell components, that can be cycled over 2400 hours at a capacity of 500 mAh/g (specific energy of about 400 Wh/kg) in an air-like atmosphere consisting of water and other air components. The developed Li-air battery cell leverages a highly active cathode catalyst, a hybrid aprotic electrolyte with two specific redox mediators, and an effective anode protection layer. Our physicochemical and electrochemical characterization of the developed Li-air battery cell indicate that lithium peroxide (Li2O2) is formed as the only discharge product formed via the solution-based mechanism and is reversibly decomposed during the charge processes. Moreover, different electrochemical experiments were performed to find out the rate capability and the deep discharge performance of the developed Li-air battery cell. We found that the designed cell components work well in synergy to deliver the lowest overpotentials reported to date for the discharge and charge (80 and 270 mV, respectively) at the first cycle, resulting in a high energy efficiency of about 90% at the first cycle. This battery design scheme offers significant promise in the advancement of sustainable energy storage systems.

Sodium-oxygen (Na-O2) batteries offer a great potential to provide high energy density storage systems needed for small-sized and inexpensive electric vehicles owing to the abundance of sodium compared with lithium. Yet, their development is hindered by the low cycle life and poor energy efficiencies due to (i) the formation of singlet oxygen, resulting in parasitic reactions with the air cathode and the organic electrolyte, (ii) the formation of unstable SEI layers and dendrites associated with the metallic sodium anode, and (iii) lack of an active, stable cathode catalyst to reduce the overpotentials and improve the cycle stability. Here, we have developed a Na-O2 battery cell composed of a highly active cathode catalyst that works well in synergy with an ether-based ionic-liquid electrolyte with specific redox mediators to act as co-catalysts to reversibly form and decompose sodium superoxide (NaO2) via surface-mediated pathway at a low polarization gap of about 40 mV at a capacity of 1000 mAh/g. Different electrochemical and physicochemical characterization techniques, i.e., Raman spectroscopy, XRD, XPS, DEMS, SEM, and TEM were used to understand the cell chemistry. Moreover, a chemically synthesized Na anode protection layer implemented in this battery cell enabled a long cycle life of 900 with all-time energy efficiencies more than 80%, exceeding state-of-art Na-O2 and Na-air batteries. The outcome of our study reveals the significance of the proper cell components design in Na-O2 battery technologies as a promising venue in energy conversion and storage systems.

An overarching challenge of the electrochemical carbon dioxide reduction reaction (eCO2RR) is finding an earth-abundant, highly active catalyst that selectively produces hydrocarbons at relatively low overpotentials. Here, we have studied the two-dimensional transition metal carbide (TMC) class of materials and found that di-tungsten carbide (W2C) nanoflakes exhibit maximum methane (CH4) current density of -421.63 mA/cm2 and a CH4 faradic efficiency of 82.7%±2% in a hybrid electrolyte of 3 M potassium hydroxide (KOH) and 2 M choline-chloride (CC). Powered by a triple junction photovoltaic cell, we have demonstrated a flow electrolyzer that uses humidified CO2 to produce CH4 in a 700-hours process under one sun illumination with a CO2RR energy efficiency of about 62.3% and a solar-to-fuel efficiency of 20.7%. Density functional theory (DFT) calculations reveal that dissociation of water, chemisorption of CO2 and cleavage of the C-O bond – the most energy consuming elementary steps in other catalysts such as copper – become nearly spontaneous at the W2C surface. This results in instantaneous formation of adsorbed CO – an important reaction intermediate – and an unlimited source of protons near the tungsten surface sites that are the main reasons for the observed superior activity, selectivity, and small potential.

The main drawbacks of today's state-of-the-art lithium-air (Li-air) batteries are their low energy efficiency and limited cycle life due to the lack of earth-abundant cathode catalysts that can drive both oxygen reduction and evolution reactions (ORR and OER) at high rates at thermodynamic potentials. Here, inexpensive trimolybdenum phosphide (Mo

Detection and analysis of volatile organic compounds' (VOCs) biomarkers lead to improvement in healthcare diagnosis and other applications such as chemical threat detection and food quality control. Here, we report on tri-molybdenum phosphide (Mo3P) and multiwalled carbon nanotube (MWCNT) junction-based vapor quantum resistive sensors (vQRSs), which exhibit more than one order of magnitude higher sensitivity and superior selectivity for biomarkers in comparison to pristine MWCNT junctions based vQRSs. Transmission electron microscope/scanning tunneling electron microscope with energy dispersive x-ray spectroscopy, x-ray diffraction, and x-ray photoelectron spectroscopy studies reveal the crystallinity and the presence of Mo and P elements in the network. The presence of Mo3P clearly enhanced the performance of vQRS as evidenced in sensitivity and selectivity studies. The vQRSs are stable over extended periods of time and are reproducible, making them a potential candidate for sensing related applications.

The electrochemical conversion of carbon dioxide to value-added products powered by renewable energies is potentially cost-effective and green method of synthesizing hydrocarbon fuels. It is also of significant interest as a strategy to reduce the concentration of atmospheric CO2 and close anthropogenic carbon cycle. An overarching challenge for this technology is developing an inexpensive and earth-abundant catalyst with high activity, stability and selectivity toward hydrocarbon fuels such as methane (CH4), methanol (CH3OH) and ethylene (C2H4). Among all type of heterogenous catalysts used for carbon dioxide reduction reaction, only copper-based catalysts have shown the ability to form hydrocarbon fuels. But they possess too low reaction rate and high overpotentials to justify their use for large-scale applications. Here, we are presenting an earth-abundant nanostructured molybdenum carbide nanoflakes (Mo2C NFs) as a highly effective catalyst for electrochemical CO2 reduction reaction. The Mo2C NFs were synthesized using a facile colloidal chemistry method followed by liquid exfoliation. The electrocatalytic performance of Mo2C NFs were carried out in a custom-made two-compartment three-electrode electrochemical cell using CO2 saturated water like buffer electrolyte and compared with Cu nanoparticles (Cu NPs) which is the conventional catalysts for electrochemical CO2 reduction reaction. The linear sweep voltammetry (LSV) results for Mo2C NFs and Cu NPs indicate that at the potential of -1.25 V vs RHE, a total current density of -138.2 mA/cm2 was obtained for Mo2C NFs while the Cu NPs show a total current density of -44.9 mA/cm2 at the same applied potential suggesting higher activity of Mo2C NFs. Our selectivity analysis, product formation faradaic efficiency (FE) measurements, show a CH4 formation onset potential of -0.45 V vs RHE for Mo2C NFs which is 500 mV less than that of Cu NPs (-0.95 V vs RHE) at identical experimental conditions. At this potential (-0.45 V vs RHE), a CH4 formation efficiency of 36.12% is recorded for Mo2C NFs that further reaches to its maximum to 51.73% at a potential of -0.65 V vs RHE while Cu NPs remain inactive for CH4 formation up to a potential of -0.95 V vs RHE, confirming higher CH4 formation selectivity of Mo2C NFs at low potentials. The results also indicate H2, CO and C2H4 production FEs of 7%, 36% and 2%, respectively, as the side products for Mo2C NFs at the potential of -0.65 V vs RHE. Moreover, our turnover frequency (TOF) calculation, actual CH4 formation activity per active site, exhibits a CH4 formation TOF of 0.4868 s-1 for Mo2C NFs that is approximately 500-times higher than Cu NFs (0.001 s-1) at the potential of -0.95 V vs RHE. We also performed different characterization methods such as X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), Raman spectroscopy and Scanning Transmission Electron Microscopy (STEM) to determine the structural and electronic properties as well as the origin of this high catalytic activity of the Mo2C NFs. The highly active and inexpensive catalyst found by this study makes it a promising candidate for effective electrochemical reduction of CO2 to CH4 that can work with renewable energy resources such as solar or wind to address ever-increasing energy demands in a sustainable pathway.

Successful demonstration of the lithium-air (Li-air) battery technology, known as a potential alternative to lithium ion batteries due to its high theoretical energy density, can contribute to electrification of transportation sector as well as solar/wind powerplants to resolve their intermittency issue. The advancement of this technology requires a cathode catalyst to drive oxygen reduction and evolution reactions (ORR and OER) happening during discharge and charge processes, respectively, at high rates at low overpotentials. This can lead to low potential gap, high efficiency, and long cycle life due to reversible formation/decomposition of lithium peroxide (Li2O2) at the cathode surface. Recently developed catalysts systems such as noble metals, bimetallic catalysts, carbon-based catalysts, transition metal oxides, and transition metal dichalcogenides have been studied to achieve such performances with incremental improvements. Here, we are presenting trimolybdenum phosphide (Mo3P) nanoparticles as an earth-abundant and stable catalyst with outstanding structural and electronic properties at surface active sites studied for ORR and OER. Our electrochemical results indicate ORR and OER current densities of 7.21 mA/cm2 at 2.0 V vs Li/Li+ (ORR) and 6.85 mA/cm2 at 4.2 V vs Li/Li+ (OER) for Mo3P nanoparticles in a non-aqueous electrolyte. Tafel plot analysis for this catalyst show slopes of 35 and 38 mV/dec for ORR and OER, respectively, suggesting a faster charge transfer kinetics, as well as ORR and OER onset potentials of 4 and 5.1 mV that are the lowest values yet reported. Moreover, our turnover frequency (TOF) calculation, actual catalytic activity, indicates up to 7 times higher activity of Mo3P nanoparticles for both ORR and OER compared to state-of-the-art catalysts used for the same application. We have tested the catalytic performance of Mo3P nanoparticles in our custom designed Li-air battery cell working at the actual air environment. The results indicate that this catalyst works perfectly together with electrolyte and lithium anode to achieve an energy efficiency of 90.2% and potential gap of 350 mV at a capacity of 500 mAh/g, surpassing the performances of state-of-the-art Li-air batteries. We have also performed various characterization techniques such as scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), in-situ differential electrochemical mass spectroscopy (DEMS) to elucidate the nature of the product in our battery cell. The results confirm fully reversible formation and decomposition of lithium peroxide (Li2O2) as the only discharge product. Furthermore, density functional theory (DFT) calculation suggests that the observed ORR and OER activities are due to the formation of a kinetically stable oxide overlayer on the Mo-terminated Mo3P (110) surface sites. The high performance, inexpensive catalyst found in our work can indeed contribute to development of efficient energy storage systems, specifically Li-air batteries, to speed up the global energy transition.

The main drawbacks of today's state-of-the-art lithium-air (Li-air) batteries are their low energy efficiency and limited cycle life due to the lack of earth-abundant cathode catalysts that can drive both oxygen reduction and evolution reactions (ORR and OER) at high rates at thermodynamic potentials. Here, inexpensive trimolybdenum phosphide (Mo3 P) nanoparticles with an exceptional activity-ORR and OER current densities of 7.21 and 6.85 mA cm-2 at 2.0 and 4.2 V versus Li/Li+ , respectively-in an oxygen-saturated non-aqueous electrolyte are reported. The Tafel plots indicate remarkably low charge transfer resistance-Tafel slopes of 35 and 38 mV dec-1 for ORR and OER, respectively-resulting in the lowest ORR overpotential of 4.0 mV and OER overpotential of 5.1 mV reported to date. Using this catalyst, a Li-air battery cell with low discharge and charge overpotentials of 80 and 270 mV, respectively, and high energy efficiency of 90.2% in the first cycle is demonstrated. A long cycle life of 1200 is also achieved for this cell. Density functional theory calculations of ORR and OER on Mo3 P (110) reveal that an oxide overlayer formed on the surface gives rise to the observed high ORR and OER electrocatalytic activity and small discharge/charge overpotentials.