OER) or only remain active for one of the reactions (different ORR/OER rates). [1-5] This can result in high overpotentials-excess energy above its thermodynamic value (2.96 V)-required to form and decompose lithium peroxide (Li 2 O 2) at the cathode during discharge (ORR) and charge (OER) processes, respectively. Numerous metal catalysts such as platinum (Pt), gold (Au), and ruthenium (Ru), as well as non-metallic catalysts such as transition-metal oxides, transition-metal dichalcogenides, and carbon-based catalysts, have been employed to resolve this issue, however, no major breakthrough has been reported to date. [4,6-11] Therefore, designing a highly active catalyst that can minimize the energy barriers-excess input energy-to form and decompose Li 2 O 2 nanoparticles at the cathode is a key challenge for the development of this technology. Electrocatalytic properties of transition metal phosphides have received great attention and been subject of theoretical and experimental studies. [12-16] Wang et al. demonstrated a convenient and straightforward approach to the synthesis of a 3D selfsupported Ni 5 P 4-Ni 2 P nanosheet cathode, very stable in acidic medium with an outstanding hydrogen evolution reaction (HER) activity. [17] Some other studies include development of 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 3 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 Mo 3 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. The advancement of lithium-air (Li-air) batteries, proposed as a potential alternative for existing energy storage systems, is mainly hampered by low energy efficiency and limited cycle life. One of the major drawbacks for today's Li-air batteries is that developed catalysts exhibit sluggish activity for both oxygen reduction and evolution reactions (ORR and

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.

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 catalyst that can also tune the selectivity toward desired products must be developed for an effective process. Here, we present oxygen functionalized copper (OFn-Cu) nanoparticles as a highly active and methane (CH4) selective catalyst for the electrocatalytic CO2 reduction reaction. Our electrochemical results indicate that OFn-Cu (5 nm) nanoparticles with an oxidized layer at the surface reach a maximum CH4 formation current density and turnover frequency of 36.24 mA/cm2 and of 0.17 s–1 at the potential of −1.05 V vs RHE, respectively, exceeding the performance of existing Cu and Cu-based catalysts. Characterization results indicate that the surface of the OFn-Cu nanoparticles consists of an oxygen functionalized layer in the form of Cu2+ (CuO) separated from the underneath elemental Cu by a Cu+ (Cu2O) sublayer. Density functional theory calculations also confirm that presence of the O site at the CuO (101) surface is the main reason for the enhanced activity and selectivity. Using this catalyst, we have demonstrated a flow cell with an active area of 25 cm2 that utilizes solar energy to produce 7.24 L of CH4 after 10 h of continuous process at a cell power density of 30 mW/cm2.

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A new porous activated carbon (AC) material with very high specific surface area (3193 m2 g−1) was prepared by the carbonization of a colloidal silica-templated melamine–formaldehyde (MF) polymer composite followed by KOH-activation. Several electrical double-layer capacitor (EDLC) cells were fabricated using this AC as the electrode material. A number of organic solvent-based electrolyte formulations were examined to optimize the EDLC performance. Both high specific discharge capacitance of 130.5 F g−1 and energy density 47.9 Wh kg−1 were achieved for the initial cycling. The long-term cycling performance was also measured.