Zhifeng Ren

• Boston College

In light of breakthroughs in superconductivity under high pressure, and considering that record critical temperatures (T c s) across various systems have been achieved under high pressure, the primary challenge for higher T c should no longer solely be to increase T c under extreme conditions but also to reduce, or ideally eliminate, the need for a...

In light of breakthroughs in superconductivity under high pressure, and considering that record critical temperatures (T$_c$s) across various systems have been achieved under high pressure, the primary challenge for higher Tc should no longer solely be to increase T$_c$ under extreme conditions but also to reduce, or ideally eliminate, the need for...

Half-Heusler compounds exhibit significant potential in thermoelectric applications for power generation up to 1000 K, notwithstanding the substantial challenges posed by the cost of constituent elements and the imperative to...

The development of highly integrated electronic components and the Internet of Things demands efficient thermal management and uninterrupted energy harvesting, which provides exciting opportunities for thermoelectric (TE) technology since it allows direct conversion between electricity and thermal energy. The improved output performance of TE devic...

Ion migration and gas diffusion are two of the most critical topics in water electrolysis. Many self-supported electrodes (SSEs) exhibit efficient performance in fundamental research studies due to their excellent gas diffusion. However, such performance is not guaranteed in large-scale electrolyzers due to the extremely large ion-migration resista...

Electronic band convergence can have a beneficial impact on thermoelectric performance, but finding the right band-converged compositions is still time-consuming. We propose a method for designing a series of compositions with simultaneous band convergence in the high-entropy Yb x Ca 1− x Mg y Zn 2− y Sb 2 material by zeroing the weighted sum of cr...

The main bottleneck in obtaining high‐performance thermoelectric (TE) materials is identified as how to decouple the strong interrelationship between electrical and thermal parameters. Herein, a precise interface modification approach based on the powder atomic layer deposition (ALD) technology is presented to enhance the performance of CuNi alloys...

The lack of desirable diffusion barrier layers currently prohibits the long-term stable service of bismuth telluride thermoelectric devices in low-grade waste heat recovery. Here we propose a new design principle of barrier layers beyond the thermal expansion matching criterion. A titanium barrier layer with loose structure is optimized, in which t...

Thermoelectric interface materials (TEiMs) are essential to the development of thermoelectric generators. Common TEiMs use pure metals or binary alloys but have performance stability issues. Conventional selection of TEiMs generally relies on trial-and-error experimentation. We developed a TEiM screening strategy that is based on phase diagram pred...

Developing non‐precious catalysts with long‐term catalytic durability and structural stability under industrial conditions is the key to practical alkaline anion exchange membrane (AEM) water electrolysis. Here we propose an energy‐saving approach to synthesize defect‐rich iron nickel oxyhydroxide for stability and efficiency toward the oxygen evol...

Studies of vacancy-mediated anomalous transport properties have flourished in diverse fields since these properties endow solid materials with fascinating photoelectric, ferroelectric, and spin-electric behaviors. Although phononic and electronic transport underpin the physical origin of thermoelectrics, vacancy has only played a stereotyped role a...

In recent decades, improvements in thermoelectric material performance have made it more practical to generate electricity from waste heat and to use solid‐state devices for refrigeration. However, despite the development of successful strategies to enhance the figure‐of‐merit zT, optimizing devices for large‐scale applications remains challenging....

NiMo-based nanostructures are among the most active hydrogen evolution reaction (HER) catalysts under an alkaline environment due to their strong water dissociation ability. However, these nanostructures are vulnerable to the destructive effects of H2 production, especially at industry-standard current densities. Therefore, developing a strategy to...

The Tauc plot method is widely used to determine the bandgap of semiconductors via UV-visible optical spectroscopy due to its simplicity and perceived accuracy. However, the actual Tauc plot often exhibits significant baseline absorption below the expected bandgap, leading to discrepancies in the calculated bandgap depending on whether the linear f...

Magnetic levitation for the transport of people and goods using bulk superconductors and electrical power transmission using superconductors have both been demonstrated, but neither has been developed for daily use due to technological deficiencies and high costs. We envision combining the transport of people and goods and energy transmission and s...

Although a high figure of merit (zT) over a wide range of temperatures has been shown in n‐type Zintl Mg3(Sb, Bi)2, further improvement of its near‐room‐temperature performance is still required to promote its application in next‐generation thermoelectric coolers and power generators. Here, a novel strategy of phonon spectra mismatch for enhancing...

To facilitate the development of thermoelectric modules for various operating temperature ranges, a connection technology that is suitable for heat-sensitive thermoelectric materials and capable of realizing both low-temperature connections and high-temperature service is required. Here we use low-temperature sintering of silver nanoparticles as an...

Irradiation can precisely control defects in, and improve the superconducting properties of, REBa2Cu3O7−δ (REBCO, RE: rare earth) coated conductors (CCs). Here we report an effective approach for enhancing the in-field performance of GdBCO CCs. The critical current density (J c) of GdBCO films was significantly improved through cooperative defects...

Studies of vacancy-mediated anomalous transport properties have flourished in diverse fields since they endow solid materials with fascinating photoelectric, ferroelectric, and spin-electric behaviors. Although phononic and electronic transport underpin the physical origin of thermoelectrics, vacancy has only played a stereotyped role as a scatteri...

Bi2Te3‐based devices have long dominated the commercial market for thermoelectric cooling applications, but their narrow operating temperature range and high cost have limited their possible applications for conversion of low‐grade heat into electric power. The recently developed n‐type Mg3Sb2‐based compounds exhibit excellent transport properties...

N-type Mg3+x(Sb, Bi)2-based thermoelectrics have quickly attracted considerable interest because of their excellent thermoelectric performance over a wide temperature range. Most studies on these compounds have thus far focused on improving their thermoelectric performance, with little consideration given to the equally essential issue of thermal s...

Cubic boron arsenide (BAs) is promising for microelectronics thermal management because of its high thermal conductivity. Recently, its potential as an optoelectronic material is also being explored. However, it remains challenging to measure its photocarrier transport properties because of small sizes of available high-quality crystals. Here, we u...

The performance of thermoelectric materials has been improved considerably in recent decades, making the concept of generating energy from waste heat via solid‐state thermoelectric devices more realistic. The construction of multi‐stage modular structures based on complex parameter optimization to maximize the efficiency of each material over its o...

Thermoelectrics is defined as direct energy conversion between the heat and electricity associated with thermoelectric power generation and refrigeration. Significant progress has been made in the theoretical understanding, materials and device preparation technology, and performance improvement of thermoelectrics since the Seebeck effect was found...

The redox couple of I0/I‐ in aqueous rechargeable iodine‐zinc (I2‐Zn) batteries is a promising energy‐storage resource since it is safe and cost‐effective, and provides steady output voltage. However, the cycle life and efficiency of these batteries remain unsatisfactory due to the uncontrolled shuttling of polyiodide (I3‐ and I5‐) and side reactio...

Seawater electrolysis for hydrogen generation has received increasing attention recently due to the scarcity of freshwater and the additional prospect of seawater desalination. The development of non-noble-metal-based oxygen evolution reaction (OER) electrocatalysts with high catalytic activity, long-term durability, and high OER selectivity is cru...

It is currently widely accepted that chemical bonding in a thermoelectric material should be weakened as much as possible to obtain a lower lattice thermal conductivity and thus a higher thermoelectric figure of merit, zT, but the consequent reliability issues, such as inferior structural stability and mechanical brittleness, are rarely emphasized....

Reliable metal alloy contact for Mg 3+ Bi 1.5 Sb 0.5 thermoelectric devices. Soft Sci 2022;2:13. https://dx. Abstract Proper contacts between thermoelectric (TE) materials and electrodes are critical for TE power generation or refrigeration. The Bi-rich n-type Zintl material Mg 3+δ Bi 2-x Sb x exhibits very good TE performance near room temperature...

p‐type CaMg2Sb2 has not been favorably considered a promising thermoelectric material in comparison to other Zintl phases. However, a series of meticulously designed tactics is successfully implemented here to analyze and improve the thermoelectric performance of a CaMg2Sb2‐based material. Band structure calculations show that the pristine CaMg2Sb2...

The thermal conductivity of boron arsenide (BAs) is believed to be influenced by phonon scattering selection rules due to its special phonon dispersion. Compression of BAs leads to significant changes in phonon dispersion, which allows for a test of first principles theories for how phonon dispersion affects three‐ and four‐phonon scattering rates....

Semiconducting cubic boron arsenide (c-BAs) has been predicted to have carrier mobility of 1400 square centimeters per volt-second for electrons and 2100 square centimeters per volt-second for holes at room temperature. Using pump-probe transient reflectivity microscopy, we monitored the diffusion of photoexcited carriers in single-crystal c-BAs to...

Semiconductors with high thermal conductivity and electron-hole mobility are of great importance for electronic and photonic devices as well as for fundamental studies. Among the ultrahigh-thermal conductivity materials, cubic boron arsenide (c-BAs) is predicted to exhibit simultaneously high electron and hole mobilities of >1000 centimeters square...

Realizing light manipulation with respect to both frequency and angular selectivity is of great significance for sunlight‐to‐heat conversion, but developing a facile and scalable method to enhance light absorption at oblique incidence remains a major challenge. Here a randomly textured absorber is theoretically designed and experimentally achieved...

Lead-free highly luminescent CsCu2I3 perovskite has attracted much attention recently, but agreements on basic optical properties have remained unsettled. By correlating X-ray diffraction with the photoluminescence (PL) of CsCu2I3 single-crystal wires, we first show that blue PL at 420 nm originates from CuI. We then exclude defect states as a sour...

In the current thermoelectric research framework, the material used to assemble a module is selected simply based on its transport properties while assuming that thermoelectric junction contact resistivity values are nearly constant for a specific material matrix, which raises concerns regarding incorrect material selection and thus deficient devic...

Cubic boron arsenide (BAs) is promising for microelectronics thermal management due to its high thermal conductivity. Recently, its potential as an optoelectronic material is also being explored. However, it remains challenging to measure its photocarrier transport properties due to small sizes of available high-quality crystals. Here, we use scann...

Recent experiments have validated prior theories of unusual high thermal conductivity (?) in boron arsenide (BAs) and revealed large ? variation associated with extended and point defects in the samples. The peak ? provides valuable insights into the competition between intrinsic phonon-phonon scattering processes and extrinsic boundary and defect...

We report a time-resolved ultrafast quasiparticle dynamics investigation of cubic boron arsenide (c-BAs), which is a recently discovered highly thermally conducting material. The excited-state ultrafast relaxation channels dictated by the electron-phonon coupling (EPC), phonon-phonon scattering, and radiative electron-hole recombination have been u...

Doping is central for solid-state devices from transistors to thermoelectric energy converters. The interaction between electrons and dopants plays a pivotal role in carrier transport. Conventional theory suggests that the Coulomb field of the ionized dopants limits the charge mobility at high carrier densities, and that either the atomic details o...

Significance Seawater is one of the most abundant resources on Earth. Direct electrolysis of seawater is a transformative technology for sustainable hydrogen production without causing freshwater scarcity. However, this technology is severely impeded by a lack of robust and active oxygen evolution reaction (OER) electrocatalysts. Here, we report a...

Exploring novel materials with intrinsically low lattice thermal conductivity (κL) is an effective way to advance thermoelectrics. Half-Heuslers (HHs) are known for their large thermoelectric power factor, but they suffer from intrinsically high κL. Their rich chemical compositions and unique atomic arrangements make possible novel HH exploration t...

Achieving efficient and durable nonprecious hydrogen evolution reaction (HER) catalysts for scaling up alkaline water/seawater electrolysis is desirable but remains a significant challenge. We demonstrate here that a heterogeneous Ni‐MoN catalyst consisting of Ni and MoN nanoparticles on amorphous MoN nanorods can sustain large‐current‐density HER...

Predictions of ultrahigh thermal conductivity in boron arsenide using first-principles calculations have motivated research to synthesize crystals and investigate their properties. In 2018, three groups reported synthesizing small single crystals of boron arsenide that exhibit thermal conductivity of 700-1300 W m-1 K-1 at room temperature. The prog...

Electrochemical reconstruction is a powerful tool for generating highly active oxygen evolution reaction (OER) catalysts. Utilizing electrochemical reconstruction to fabricate an OER active catalyst based on a hydrogen evolution reaction...

The catalytic hydrogen‐evolving activities of transition‐metal phosphides are greatly related to the phosphorus content, but the physical origin of performance enhancement remains ambiguous, and tuning the catalytic activity of nickel phosphides (NiP2/Ni5P4) remains challenging due to unfavorable H* adsorption. Here, a strategy is introduced to int...

Minimizing the lattice thermal conductivity of thermoelectric materials is essential for preserving the temperature difference during the operation of thermoelectric devices incorporating these materials. During the past two decades, there has been substantial improvement in the thermoelectric figure of merit (zT) due to reduced lattice thermal con...

Hydrogen generation by seawater electrolysis is a sustainable approach to renewable-energy conversion which requires efficient catalyst to address challenges such as competing chlorine evolution reaction, chloride corrosion, and catalyst poisoning. Here, core-shell-structured CoPx@FeOOH is designed for selective OER in seawater. This catalyst has h...

Mg3Sb2-based Zintl compounds have attracted extensive attention as potential thermoelectric materials due to their earth-abundant elements. However, pure and intrinsic p-type Mg3Sb2 manifests a poor thermoelectric performance because of its high electrical resistivity. It is reported that Ag doping in Mg sites can increase the mobility and carrier...

Achieving superconducting joinings with large current capacities is a challenge for magnetic resonance imaging applications of YBa2Cu3O7-δ (YBCO) coated conductors (CCs). Here we report a novel method to fabricate a superconducting joining between two YBCO CCs using a joining strap consisting of YBCO, Ag, a buffer, and a substrate. The YBCO layer e...

Since 2015, when we first reported that the half-Heusler alloy NbCoSb with a nominal 19-valence-electrons composition exhibits the moderate thermoelectric properties of a heavily doped n-type semiconductor, we have been studying the preparation of pure-phase materials. Here we report, for the first time, the effects of Nb and Sb deficiencies on the...

As an essential feedstock for fertilizer and chemical industries, ammonia is being produced by a so-called Haber-Bosch process. However, global warming and the energy crisis urge us to find a sustainable and clean alternative for ammonia production. Photocatalytic nitrogen fixation is an alternative but challenging method. Low reactivity of nitroge...

The unusually high lattice thermal conductivity of semiconducting cubic boron arsenide (BAs) has motivated studies of the bulk electronic band structure of BAs for its potential use as an active layer material in electronic devices. However, the surface electronic structure of BAs remains to be investigated. Scanning tunneling spectroscopy (STS) is...

In an effort to improve the thermoelectric performance of the environmentally friendly SnTe, here, a multilevel structure composed of “lotus‐seedpod‐like” grain boundaries, dense dislocations, and nanopores is innovatively constructed, which synergistically reduces the sound velocity and the phonon relaxation time, resulting in ultralow lattice the...

Rechargeable aqueous Zn-based batteries are highly desirable for future applications in large-scale energy storage since they are inexpensive and safe in comparison with lithium-ion batteries (LIBs). Additionally, the high energy density of Zn batteries, nearly comparable to that of LIBs, stands out in all types of aqueous batteries. Fast charge, e...

Recently, flexible thermoelectric (TE) materials and devices have attracted extensive attention due to their capability to convert heat into electricity directly and their conformal contact with arbitrarily shaped heat sources, demonstrating great promise for application in selfpowered portable/wearable low power consuming electronics. Here, we rev...

Developing and understanding novel doping strategies for thermoelectric materials is imperative to efficiently convert waste into a useful voltage. One such method for improving the power factor of polymer nanocomposites is through salt doping. The cation size of a monovalent salt dopant was varied in a layer-by-layer (LbL)-assembled film composed...

Low-grade heat harvesting by thermoelectric technology can contribute to efficient energy utilization. However, the large-scale application of thermoelectric devices is partially hindered by their unsatisfactory performance and relatively high cost. Here we prepared a cost-effective n-type Mg3Bi2-based compound with a peak zT of 1.24 at 573 K. A un...

Electrochemical seawater splitting is a promising technique because it addresses two major challenges, clean energy production and seawater desalination, at the same time. Therefore, seeking out a facile and cost-effective way to synthesize highly active and stable seawater-splitting catalysts is of great interest to both the research community and...

Nanoscale composites for high‐performance electrodes employed in flexible, all‐solid‐state supercapacitors are being developed. A series of binder‐free composites, each consisting of a transition bimetal oxide, a metal oxide, and a metal nitride grown on N‐doped reduced graphene oxide (rGO)‐wrapped nickel foam are obtained by using a universal stra...

Materials with interfaces often exhibit extraordinary phenomena exemplified by rich physics, such as high-temperature superconductivity and enhanced electronic correlations. However, demonstrations of confined interfaces to date have involved intensive effort and fortuity, and no simple path is consistently available. Here, we report the achievemen...

In a traditional thermoelectric π-type module, there is severe thermal stress at the hot side due to the thermal expansion of the hot-side ceramic plate and the mismatch between the coefficient of thermal expansion values among the different components, resulting in the likely development of permeant strain in the module, which leads to short lifet...

Water electrolysis provides a promising route to produce high energy density hydrogen. Compared with the limited amount of fresh water, seawater is an abundant resource that has attracted increasing attention for electrolysis. However, seawater electrolysis has thus far suffered from degraded activity and stability, and from low oxygen evolution re...

Thermoelectric technology converts heat into electricity directly and is a promising source of clean electricity. Commercial thermoelectric modules have relied on Bi2Te3-based compounds because of their unparalleled thermoelectric properties at temperatures associated with low-grade heat (<550 K). However, the scarcity of elemental Te greatly limit...

Bi2Te3 based alloys have been the most widely used thermoelectric material at low temperature for many decades. Here we report Se doped n-type Mg3Bi2 based materials with a thermoelectric figure-of-merit ZT of 0.82 at 300 K and a peak ZT of 1.24 at 498 K, which is comparable to the n-type Bi2Te3 and Te doped Mg3Bi1.4Sb0.6. The improved thermoelectr...

Developing efficient and stable oxygen evolution reaction (OER) catalysts that can work well at high current densities for seawater electrolysis is desirable but remains a significant challenge. Here a novel and scalable strategy is developed to synthesize partially amorphous boron-modified cobalt iron layered double hydroxides (B-Co2Fe LDH). Benef...

We report ⁹³Nb and ¹²¹Sb NMR and ⁵⁷Fe Mössbauer studies combined with DFT calculations of Nb1−xTixFeSb (0 ≤ x ≤ 0.3), one of the most promising thermoelectric systems for applications above 1000 K. These studies provide local information about defects and electronic configurations in these heavily p-type materials. The NMR spin-lattice relaxation r...

Solid-state thermoelectric devices can directly convert electricity into cooling or enable heat pumping through the Peltier effect. The commercialization of thermoelectric cooling technology has been built on the Bi2Te3 alloys, which have had no rival for the past six decades around room temperature. With the discovery and development of more promi...

The highly efficient n-type Mg3Sb2-xBix thermoelectric materials hold great promise for application in power generation as well as refrigeration. Currently, n-type Mg3Sb2-xBix compounds with high zTs can be easily reproduced on a laboratory scale with ∼10 g per batch. However, scaling up the synthesis of Mg3Sb2-xBix with uniform high thermoelectric...

N-type Mg3Sb2-x Bi x alloys have been extensively studied in recent years due to their significantly enhanced thermoelectric figure of merit (zT), thus promoting them as potential candidates for waste heat recovery and cooling applications. In this review, the effects resulting from alloying Mg3Bi2 with Mg3Sb2, including narrowed bandgap, decrease...

The recently discovered n-type Mg3Sb2-xBix alloys with high thermoelectric performance hold great potential for applications in waste heat recovery due to their high average zT in the temperature range between 300 and 773 K. However, systematic studies of their thermal stability remain lacking and are significant for these thermoelectric materials...

Pickering emulsions show great promise for many applications in the oil and gas industry. However, the thermal stability of Pickering emulsions reported thus far has been unfavorable for safe operation in the always high-temperature deep underground condition. Here we report a Pickering water-in-oil (W/O) emulsion that exhibits high temperature tol...

Developing high‐performance and cost‐effective bifunctional electrocatalysts for large‐scale water electrolysis is desirable but remains a significant challenge. Most existing nano‐ and micro‐structured electrocatalysts require complex synthetic procedures, making scale‐up highly challenging. Here, a heterogeneous Ni2P‐Fe2P microsheet is synthesize...

Artificial photosynthesis of ammonia using atmospheric nitrogen and water is a sustainable but challenging alternative to the Haber-Bosch process. Bismuth oxyiodide (BiOI) is a promising candidate due to its superior light absorption capability (bandgap of around 1.8 eV) and abundant surface oxygen vacancies. However, its improper band edge positio...

As reserves of conventional light oil become depleted, recovery of viscous oil is urgently needed to meet increasing energy demands worldwide before clean energy sources are fully developed. Current oil extraction technologies suffer from low efficiency, high cost, and environmental concerns. Attempts to use nanotechnology in this field have thus f...

We report 59 Co, 93 Nb, and 121 Sb nuclear magnetic resonance measurements combined with density functional theory (DFT) calculations on a series of half-Heusler semiconductors, including NbCoSn, ZrCoSb, TaFeSb, and NbFeSb, to better understand their electronic properties and general composition-dependent trends. These materials are of interest as...

AgCuTe has been recognized as a promising thermoelectric material due to its reported ultralow lattice thermal conductivity, but its phase transition and unsatisfactory thermoelectric performance at close to room temperature restrict its application for the harvesting of low-grade heat. In this work, the near-room-temperature phase transition is su...

Seawater electrolysis presents a transformative technology for sustainable hydrogen production and environmental remediation. However, the lack of active and robust hydrogen evolution reaction (HER) catalysts severely impedes the development of this technology. Here, we report a sandwich-like nanostructured HER catalyst constructed by decorating bo...