Xijun Liu

Potential-Cycling Synthesis of Single Platinum Atoms for Efficient Hydrogen Evolution in Neutral Media

Abstract Single‐atom catalysts (SACs) have exhibited high activities for the hydrogen evolution reaction (HER) electrocatalysis in acidic or alkaline media, when they are used with binders on cathodes. However, to date, no SACs have been reported for the HER electrocatalysis in neutral media. We demonstrate a potential‐cycling method to synthesize a catalyst comprising single Pt atoms on CoP‐based nanotube arrays supported by a Ni foam, termed PtSA‐NT‐NF. This binder‐free catalyst is centimeter‐scale and scalable. It is directly used as HER cathodes, whose performances at low and high current densities in phosphate buffer solutions (pH 7.2) are comparable to and better than, respectively, those of commercial Pt/C. The Pt mass activity of PtSA‐NT‐NF is 4 times of that of Pt/C, and its electrocatalytic stability is also better than that of Pt/C. This work provides a large‐scale production strategy for binder‐free Pt SAC electrodes for efficient HER in neutral media.

WO3@α-Fe2O3 Heterojunction Arrays with Improved Photoelectrochemical Behavior for Neutral pH Water Splitting

Photoelectrochemical (PEC) water splitting on illuminated semiconductors plays an increasing role in alternative energy devices because of the need for clean and sustainable energy. However, the overall efficiency of the process is still very low and requires further improvement for widespread application. Herein, we report that the PEC performance of WO3 can be optimized by constructing a WO3@α‐Fe2O3 heterojunction nanosheet array to expand the spectral range of light absorption and promote photogenerated electron–hole separation/transfer. This heterojunction photoanode exhibit a pronounced photocurrent response of 1.66 mA cm−2, a high incident photon‐to‐current conversion efficiency of ∼73.7 % at 390 nm, and an excellent photostability of 100 %, all at 1.23 V versus reversible hydrogen electrode. Therefore, our approach has great potential for designing efficient hybrid photoanodes for PEC water‐splitting systems.

Efficient and stable electroreduction of CO2 to CH4 on CuS nanosheet arrays

Converting CO2 into value-added hydrocarbon fuels has attracted enormous interest due to the advantage of simultaneously addressing major energy and environmental issues. Here we report on copper sulfide nanosheet arrays supported on nickel foam (CuS@NF) applied as a robust catalyst for CO2 electroreduction. A high faradaic efficiency of 73 ± 5% and a low Tafel slope of 57 mV dec−1 for CH4 formation were achieved. Moreover, the CuS nanosheets showed a stable CO2 electroreduction capability up to 60 h. The high performance of CuS@NF for CO2 electroreduction was ascribed to the nanosheet morphology as well as the presence of S species. This work illustrates how to design efficient and stable copper chalcogenide electrocatalysts for generating carbon-based fuels.

Highly Active, Durable Ultrathin MoTe2 Layers for the Electroreduction of CO2 to CH4

The electroreduction of CO2 to CH4 is a highly desirable, challenging research topic. In this study, an electrocatalytic system comprising ultrathin MoTe2 layers and an ionic liquid electrolyte for the reduction of CO2 to methane is reported, efficiently affording methane with a faradaic efficiency of 83 ± 3% (similar to the best Cu-based catalysts reported thus far) and a durable activity of greater than 45 h at a relatively high current density of 25.6 mA cm-2 (-1.0 VRHE ). The results obtained can facilitate research on the design of other transition-metal dichalcogenide electrocatalysts for the reduction of CO2 to valuable fuels.

Two-in-one solution using insect wings to produce graphene-graphite films for efficient electrocatalysis

Natural organisms contain rich elements and naturally optimized smart structures, both of which have inspired various innovative concepts and designs in human society. In particular, several natural organisms have been used as element sources to synthesize low-cost and environmentally friendly electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells and metal–air batteries, which are clean energy devices. However, to date, no naturally optimized smart structures have been employed in the synthesis of ORR catalysts, including graphene-based materials. Here, we demonstrate a novel strategy to synthesize graphene–graphite films (GGFs) by heating butterfly wings coated with FeCl3 in N2, in which the full power of natural organisms is utilized. The wings work not only as an element source for GGF generation but also as a porous supporting structure for effective nitrogen doping, two-dimensional spreading, and double-face exposure of the GGFs. These GGFs exhibit a half-wave potential of 0.942 V and a H2O2 yield of < 0.07% for ORR electrocatalysis; these values are comparable to those for the best commercial Pt/C and all previously reported ORR catalysts in alkaline media. This two-in-one strategy is also successful with cicada and dragonfly wings, indicating that it is a universal, green, and cost-effective method for developing high-performance graphene-based materials.

Self-powered H 2 production with bifunctional hydrazine as sole consumable

Splitting hydrazine into H2 and N2 by electro-catalyzing hydrogen evolution and hydrazine oxidation reactions is promising for replacing fossil energy with H2. However, current hydrazine splitting is achieved using external powers to drive the two reactions, which is inapplicable to outdoor use. Here, Fe-doped CoS2 nanosheets are developed as a bifunctional electrocatalyst for the two reactions, by which direct hydrazine fuel cells and overall-hydrazine-splitting units are realized and integrated to form a self-powered H2 production system. Without external powers, this system employs hydrazine bifunctionally as the fuel of direct hydrazine fuel cell and the splitting target, namely a sole consumable, and exhibits an H2 evolution rate of 9.95 mmol h−1, a 98% Faradaic efficiency and a 20-h stability, all comparable to the best reported for self-powered water splitting. These performances are due to that Fe doping decreases the free-energy changes of H adsorption and adsorbed NH2NH2 dehydrogenation on CoS2.While water electrolysis provides an attractive means to produce high-energy hydrogen (H2), the process imposes significant material overpotential barriers. Here, authors employ the more-facile hydrazine splitting reaction, coupled to a hydrazine fuel cell, to perform self-powered H2 evolution.

Stepped surface-rich copper fiber felt as an efficient electrocatalyst for the CO2RR to formate

Copper (Cu) electrocatalysts for the carbon dioxide reduction reaction (CO2RR) attract immense interest by virtue of their low cost, environmental suitability and the ability to produce diverse reduction products. However, to date, realizing high selectivity for formate on Cu electrocatalysts in water-based electrolytes remains a significant challenge. Herein, we first synthesized Cu fiber felt as an efficient and stable electrocatalyst for the CO2RR through a novel biomass carbon-templated route. Remarkably, the Cu fibers expose rich nano-scale stepped surfaces with the preferred {111} facets, endowing the Cu fiber felt with high catalytic activity for formate formation, whose faradaic efficiency reaches 71.1 ± 3.1% in aqueous potassium hydrogencarbonate solution. Meanwhile, the Cu fiber felt exhibits good stability over 390 min of electrolysis. The present work potentially provides a new avenue of surface nanostructure design for more efficient and selective Cu electrocatalysts for the CO2RR.