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.

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

Conversion of CO2 to energy‐rich chemicals using renewable energy is of much interest to close the anthropogenic carbon cycle. However, the current photoelectrochemical systems are still far from being practically feasible. Here the successful demonstration of a continuous, energy efficient, and scalable solar‐driven CO2 reduction process based on earth‐abundant molybdenum disulfide (MoS2) catalyst, which works in synergy with an inexpensive hybrid electrolyte of choline chloride (a common food additive for livestock) and potassium hydroxide (KOH) is reported. The CO2 saturated hybrid electrolyte utilized in this study also acts as a buffer solution (pH ≈ 7.6) to adjust pH during the reactions. This study reveals that this system can efficiently convert CO2 to CO with solar‐to‐fuel and catalytic conversion efficiencies of 23% and 83%, respectively. Using density functional theory calculations, a new reaction mechanism in which the water molecules near the MoS2 cathode act as proton donors to facilitate the CO2 reduction process by MoS2 catalyst is proposed. This demonstration of a continuous, cost‐effective, and energy efficient solar driven CO2 conversion process is a key step toward the industrialization of this technology.

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.

candidates to replace precious metal catalysts owing to the unique electronic properties of their edge structures. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] However, the basal plane of these catalysts containing substantial amount of their surface structure remains nearly inactive making these catalysts inefficient, especially for practical applications. [26][27][28][29] Therefore, designing and developing a new class of nonprecious metal catalysts with an increased intrinsic activity that concurrently hold a high number of active sites still remain as a challenging task in the field of electrocatalysis.Here, we have found nanostructured trimolybdenum phosphide (Mo 3 P) as a novel material for solid-state electrocatalytic reactions owing to its high density of active sites with outstanding electronic properties. We have tested the performance of this catalyst in the electrochemical hydrogen evolution reaction (HER) and compared with Pt, known as the best HER catalyst. Cyclic voltammetry (CV) and in situ differential electrochemical mass spectroscopy (DEMS) results illustrate onset potential of as low as 21 mV that is the closest value to Pt yet reported. [30] The onset potential is also seven, four, and three times lower than other recently developed nonprecious metal catalysts, i.e., MoS 2 , Mo 2 C, and molybdenum phosphide (MoP) nanoflakes (NFs), respectively. [31,32] The turnover frequency (TOF) measurements, actual activity of surface atoms, at 150 mV overpotential also offer 21.5-fold activity improvement for the Mo 3 P catalyst than that of MoS 2 NFs. Atomic-scale characterization Solid-state electrocatalysis plays a crucial role in the development of renewable energy to reshape current and future energy needs. However, finding an inexpensive and highly active catalyst to replace precious metals remains a big challenge for this technology. Here, tri-molybdenum phosphide (Mo 3 P) is found as a promising nonprecious metal and earthabundant candidate with outstanding catalytic properties that can be used for electrocatalytic processes. The catalytic performance of Mo 3 P nanoparticles is tested in the hydrogen evolution reaction (HER). The results indicate an onset potential of as low as 21 mV, H 2 formation rate, and exchange current density of 214.7 µmol s −1 g −1 cat (at only 100 mV overpotential) and 279.07 µA cm −2 , respectively, which are among the closest values yet observed to platinum. Combined atomic-scale characterizations and computational studies confirm that high density of molybdenum (Mo) active sites at the surface with superior intrinsic electronic properties are mainly responsible for the remarkable HER performance. The density functional theory calculation results also confirm that the exceptional performance of Mo 3 P is due to neutral Gibbs free energy (ΔG H *) of the hydrogen (H) adsorption at above 1/2 monolayer (ML) coverage of the (110) surface, exceeding the performance of existing non-noble metal catalysts for HER.