Over the years, cobalt phosphates (amorphous or crystalline) have been projected as one of the most significant and promising classes of nonprecious catalysts and studied exclusively for the ...electrocatalytic and photocatalytic oxygen evolution reaction (OER). However, their successful utilization of hydrogen evolution reaction (HER) and the reaction of overall water‐splitting is rather unexplored. Herein, presented is a crystalline cobalt phosphate, Co3(OH)2(HPO4)2, structurally related to the mineral lazulite, as an efficient precatalyst for OER, HER, and water electrolysis in alkaline media. During both electrochemical OER and HER, the Co3(OH)2(HPO4)2 nanostructure was completely transformed in situ into porous amorphous CoOx
(OH) films that mediate efficient OER and HER with extremely low overpotentials of only 182 and 87 mV, respectively, at a current density of 10 mA cm−2. When assemble as anode and cathode in a two‐electrode alkaline electrolyzer, unceasing durability over 10 days is achieved with a final cell voltage of 1.54 V, which is superior to the recently reported effective bifunctional electrocatalysts. The strategy to achieve more active sites for oxygen and hydrogen generation via in situ oxidation or reduction from a well‐defined inorganic material provides an opportunity to develop cost‐effective and efficient electrocatalysts for renewable energy technologies.
A crystalline lazulite cobalt phosphate is identified as a low‐cost preelectrocatalyst for generating remarkably active and durable electrocatalysts for unifying the hydrogen evolution reaction, oxygen evolution reaction, and overall water‐splitting in alkaline media. Under oxidizing and reducing electrochemical environments, the restructuring (corrosion) of highly crystalline particles results in two different in situ‐generated amorphously active phases, yielding low overpotentials and cell potential.
A fast and facile route for the optimization of covalent triazine frameworks (CTFs) for photocatalytic hydrogen production is presented. Within 10 minutes a CTF with low photocatalytic activity can ...be converted into a highly active photocatalyst. Optimized CTF catalysts show an average hydrogen evolution rate of 1072 μmol h
g
under visible light (>420 nm).
Covalent organic frameworks (COFs) have emerged as an important class of organic semiconductors and photocatalysts for the hydrogen evolution reaction (HER)from water. To optimize their ...photocatalytic activity, typically the organic moieties constituting the frameworks are considered and the most suitable combinations of them are searched for. However, the effect of the covalent linkage between these moieties on the photocatalytic performance has rarely been studied. Herein, we demonstrate that donor‐acceptor (D‐A) type imine‐linked COFs can produce hydrogen with a rate as high as 20.7 mmol g−1 h−1 under visible light irradiation, upon protonation of their imine linkages. A significant red‐shift in light absorbance, largely improved charge separation efficiency, and an increase in hydrophilicity triggered by protonation of the Schiff‐base moieties in the imine‐linked COFs, are responsible for the improved photocatalytic performance.
Protonation of imine‐linked COFs yields significant variations of their (opto)electronic properties and results in a largely enhanced performance in photocatalytic hydrogen evolution from water. This is attributed to an enhanced light absorption ability, charge separation efficiency, and hydrophilicity of imine‐linked COFs upon protonation.
The design and development of economical and highly efficient electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under alkaline conditions are vital in ...lowering the overall energy losses in alkaline water electrolysis. Here we present a nickel phosphite, Ni 11 (HPO 3 ) 8 (OH) 6 , belonging to the unique class of phosphorus-based inorganic materials with striking structural features that have been explored for the first time in the reaction of electrocatalytic overall water splitting with a profound understanding of the system using in situ and ex situ techniques. When electrophoretically deposited, the nickel phosphite exhibited remarkable electrocatalytic activity, yielding considerably low overpotentials for both the OER and HER with extreme structural stability and enhanced durability in alkaline media. Apart from the attractive structural merits, the higher activity of nickel phosphite is mainly attributed to the formation of oxidized nickel species in the catalytic OER process, while subtle experimental evidence of the participation of phosphite anions for the acceleration of the HER with the support of Ni 2+ cations as catalytically active sites is identified, which is highly compelling and has never been previously discovered. Finally, the bifunctionality of nickel phosphite was demonstrated by constructing an alkaline water electrolyzer with a low cell voltage and over 4 days of undiminishing stability. This work offers an appealing cost-effective system based on earth-abundant metals for water electrolysis and can be extended to other transition metal based homo- or hetero-bimetallic phosphites.
Yes, we CAN: Partial oxidation of inactive MnO nanoparticles by CeIV as oxidant gives active MnOx catalysts that are suitable for effective photochemical and electrochemical water oxidation. The ...active MnOx catalyst contains mixed‐valent MnII, MnIII, and MnIV species (see picture; green and violet) interconnected through oxido bridges (red) with defects and disorders. MnOx is analogous to calcium–manganese oxide systems where the calcium sites are replaced by MnII or MnIII ions.
Photoelectrochemical water splitting in near-neutral pH conditions offers a safe and sustainable way to produce solar fuels, but operation at near-neutral pH is challenging because of the added ...concentration overpotentials due to mass-transport limitations of protons and hydroxide ions. Understanding the extent of this limitation is essential in designing a highly efficient solar fuel conversion device. In the present study, the local pH between the anode and cathode in a water splitting cell is monitored in situ using fluorescence pH sensor foils. By this direct visualization, we confirm that supporting buffer ions effectively suppress local pH changes, and we show that electrochemical reactions induce natural electrolyte convection in a non-stirred cell. The observed electrolyte convection at low current densities (<2 mA cm −2 ) originates from buoyancy effects due to the change in the local electrolyte density by ion depletion and accumulation. A multiphysics simulation that includes the buoyancy effect reveals that natural convection driven by electrochemical reactions stabilizes the local pH, which is consistent with our experimental observations. In contrast, the model without the buoyancy effect predicts significant shifts of the local pH away from the p K a of the buffer, even at low current densities. This experimentally validated model reveals that natural convection induced by electrochemical reactions significantly affects the overall mass-transport, especially in close vicinity of the electrodes, and it should, therefore, be considered in the design and evaluation of solar fuel conversion devices.
Abstract
Green hydrogen has been identified as a critical enabler in the global transition to sustainable energy and decarbonized society, but it is still not economically competitive compared to ...fossil-fuel-based hydrogen. To overcome this limitation, we propose to couple photoelectrochemical (PEC) water splitting with the hydrogenation of chemicals. Here, we evaluate the potential of co-producing hydrogen and methyl succinic acid (MSA) by coupling the hydrogenation of itaconic acid (IA) inside a PEC water splitting device. A negative net energy balance is predicted to be achieved when the device generates only hydrogen, but energy breakeven can already be achieved when a small ratio (
~
2%) of the generated hydrogen is used in situ for IA-to-MSA conversion. Moreover, the simulated coupled device produces MSA with much lower cumulative energy demand than conventional hydrogenation. Overall, the coupled hydrogenation concept offers an attractive approach to increase the viability of PEC water splitting while at the same time decarbonizing valuable chemical production.
In orthopaedic research, the analysis of the gait pattern is an often-used evaluation method. It allows an assessment of changes in motion sequence and pain level during postoperative follow up ...periods. Visual assessments are highly subjective and dependent on the circumstances. Particular challenge in rabbits is their hopping gait pattern. The aim of the present study was to establish a more objective and sensitive lameness evaluation using a pressure sensing mat. Twelve NZW rabbits were implemented in the study. They got an artificial anterior cruciate ligament transection of the right knee in connection with an experimental study, which investigated PTOA treatment. Rabbits were examined by a visual lameness score. Additionally, load of the hindlimbs was measured by the use of a pressure sensing mat and a video was recorded. Peak pressure and time force integral, defined as cumulated integral of all sensors associated to a hind paw, were evaluated. Preoperative data were collected on three independent days. As postoperative measurement time points, week 1 and week 12 after surgery were chosen. The subjective visual scoring was compared to the objective data of the pressure sensing mat. Following the visual score, lameness in week one was mild to moderate. In week twelve, rabbits were evaluated as lame free bar one. Contrary, following the values of the sensor mat, lameness in week one appeared to be more pronounced and almost all rabbits still showed low-grade lameness in week twelve. Consequently, the pressure sensing mat is more sensitive than the visual score and captures the grade of lameness much more accurately. For specific orthopaedic issues, where subtle differences in lameness are important to detect, the used system is a good supplementary evaluation method.
Many years ago, twelve principles were defined for carrying out chemical reactions and processes from a green chemistry perspective. It is everyone's endeavor to take these points into account as far ...as possible when developing new processes or improving existing ones. Especially in the field of organic synthesis, a new area of research has thus been established: micellar catalysis. This review article addresses the question of whether micellar catalysis is green chemistry by applying the twelve principles to micellar reaction media. The review shows that many reactions can be transferred from an organic solvent to a micellar medium, but that the surfactant also has a crucial role as a solubilizer. Thus, the reactions can be carried out in a much more environmentally friendly manner and with less risk. Moreover, surfactants are being reformulated in their design, synthesis, and degradation to add extra advantages to micellar catalysis to match all the twelve principles of green chemistry.
Display omitted
•Pt/C-TiO2 (0.5–3.0 wt.%) photocatalysts were synthesized by photodeposition method.•Structure and morphology of investigated photocatalysts were thoroughly analyzed.•The ...photocatalysts were examined for CO2 photocatalytic reduction in gas phase.•Enhanced photocatalytic activity of photocatalyst can be attributed to the low electron-hole recombination.
Photocatalytic reduction of CO2 with H2O was performed in a top-irradiation stainless-steel photoreactor with Pt/C-TiO2 as the photocatalyst. Pt/C-TiO2 photocatalysts with different amount of Pt (0.5–3.0 wt.%) were synthesized by the photodeposition method and were characterized in detail by X-ray powder diffraction (XRD), nitrogen physisorption measurement (BET), UV–vis diffuse reflectance spectroscopy, inductively coupled plasma optical emission spectrometry (ICP-OES), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoelectrochemical measurements. Results revealed the photocatalytic reduction of CO2 increased by loading Pt on the surface of C-TiO2. The main reaction product was methane (CH4), however, hydrogen (H2) and carbon monoxide (CO) were also detected. The highest yields of CH4, H2, and CO were achieved in the presence Pt/C-TiO2 with a nominal loading of 0.88 wt.%, resulting from the efficient interfacial transfer of photogenerated electrons from C-TiO2 to Pt as it is evidenced from photoelectochemical measurements.
PDF
