Kasper Wenderich

Bio: Kasper Wenderich is an academic researcher from MESA+ Institute for Nanotechnology. The author has contributed to research in topics: Platinum nanoparticles & Oxidation state. The author has an hindex of 7, co-authored 13 publications receiving 573 citations. Previous affiliations of Kasper Wenderich include Martin Luther University of Halle-Wittenberg & University of Twente.

Methods, Mechanism, and Applications of Photodeposition in Photocatalysis: A Review.

Abstract: In this review, for a variety of metals and semiconductors, an attempt is made to generalize observations in the literature on the effect of process conditions applied during photodeposition on (i) particle size distributions, (ii) oxidation states of the metals obtained, and (iii) consequences for photocatalytic activities. Process parameters include presence or absence of (organic) sacrificial agents, applied pH, presence or absence of an air/inert atmosphere, metal precursor type and concentration, and temperature. Most intensively reviewed are studies concerning (i) TiO2; (ii) ZnO, focusing on Ag deposition; (iii) WO3, with a strong emphasis on the photodeposition of Pt; and (iv) CdS, again with a focus on deposition of Pt. Furthermore, a detailed overview is given of achievements in structure-directed photodeposition, which could ultimately be employed to obtain highly effective photocatalytic materials. Finally, we provide suggestions for improvements in description of the photodeposition methods applied when included in scientific papers.

Sorption‐Determined Deposition of Platinum on Well‐Defined Platelike WO3

Abstract: The photodeposition of Pt nanoparticles from [PtCl6]2− on platelike WO3 crystals occurs preferentially on the small, subordinate facets. Rather than the often-used explanation of preferred light-induced charge migration, we propose that this phenomenon is due to differences in the intrinsic surface charges of WO3 facets exposed to water; thus, the dark sorption of [PtCl6]2− on positively charged facets/edges is preferred. This conclusion is based on 1) (dark) impregnation studies, which showed Pt deposition to also be facet-specific, and 2) aqueous-phase AFM studies, which suggest intrinsic surface charges to be in agreement with sorption-based Pt distributions

Time-Dependent Photoluminescence of Nanostructured Anatase TiO2 and the Role of Bulk and Surface Processes

Abstract: TiO2 is one of the most attractive photocatalysts, with applications in water splitting, wastewater treatment, and air purification. Understanding the fundamentals of the functioning of TiO2 requires knowledge of the nature and dynamics of photo-induced excitons and charge carriers. Although photoluminescence (PL) spectroscopy can provide important fundamental insights, photophysical mechanisms are still under debate. To address this problem, the aim of the present work is to investigate the evolution of the PL spectrum in time of nanostructured anatase TiO2 thin films and the nature of associated processes, at room temperature and in aqueous media closely resembling photocatalytic conditions. We show that the PL spectrum of commonly used nanostructured anatase TiO2 thin films in aqueous media is time-dependent, with pH-dependent broadening at the low energy side of the spectrum in time. By global analysis of the spectrotemporal PL behavior and the effect of addition of NaCl at neutral and mildly acidic conditions, we show that this spectral development is due to an increasing contribution of processes sensitive to surface termination relative to bulk processes to the PL in time. The time-dependent PL spectrum and dynamics can be assigned to the recombination of mobile electrons populating the conduction band or shallow traps with immobile hole polarons in deep traps and motion of electrons from the nanoparticle bulk toward the depletion layer/surface in ca. 1 ns. This directionality likely plays an important role in the photocatalytic performance of nanostructured anatase TiO2 and effects of ions such as chloride in aqueous media. Control of the directional motion of electrons and suppression of surface charge recombination via surface engineering show promise to further increase the photocatalytic activity.

Selective Electrochemical Oxidation of H2O to H2O2 using Boron-doped diamond: an experimental and techno-economic evaluation

Abstract: Selective water oxidation to hydrogen peroxide has emerged as an economically attractive replacement for oxygen in electrochemical hydrogen production by water splitting. Here, boron-doped diamond (BDD) is shown to be a promising anode material for anodic H2O2 formation. Faradaic efficiencies of up to 31.7% at 2.90 V versus the reference hydrogen electrode and a current density of 39.8 mA cm–2 were observed, corresponding to a H2O2 production rate of 3.93 μmol min–1 cm–2. A techno-economic evaluation based on the experimentally obtained values demonstrates that the corresponding levelized cost of hydrogen (LCH) is significant ($62.0 kg–1). Particularly, the current market price of BDD limits its implementation as a selective water oxidation anode for H2O2 generation. The sensitivity analysis however suggests that the LCH can be significantly improved by either decreasing the anode cost or increasing the current density. Both approaches are in fact feasible to allow for cost-effective electrochemical H2 production and even competition with H2 obtained from steam methane reforming. This study will guide ongoing research efforts toward BDD development and implementation of selective water oxidation to hydrogen peroxide.

Industrial feasibility of anodic hydrogen peroxide production through photoelectrochemical water splitting: a techno-economic analysis

Abstract: Photoelectrochemical (PEC) water splitting is a promising approach to drive green, carbon-free production of hydrogen (H2). In ‘classic’ water splitting, oxygen (O2) is formed at the anode as a by-product. It has been suggested that substitution of anodic O2 production with hydrogen peroxide (H2O2) could increase the financial attractiveness of PEC water splitting. Here, we present a techno-economic analysis of a photoelectrochemical H2/H2O2 process. Specifically, we model photoelectrochemical farms with industrially relevant production capacities. Two scenarios are considered: (i) a theoretical scenario with an optimal solar-to-hydrogen (STH) efficiency of 27.55% and (ii) a literature-based state-of-the-art scenario with an STH efficiency of 10.1%. When applying an averaged market value of $0.85 kg−1 for H2O2, the analysis reveals a negative levelized cost of hydrogen (LCH) for scenario (i), i.e. $6.45 kg−1, and for scenario (ii) an LCH of $6.19 kg−1. Our results imply that these values are superior to the LCH of ‘classic’ PEC water splitting (ca. $10 kg−1), while the negative value for scenario (i) even outcompetes the LCH of steam methane reforming ($1.4 kg−1). We predict that significant reduction in the LCH can be realized within the PEC community when future research is aimed at enhancing the stability of the photoanode and optimizing the STH efficiency for anodic H2O2 formation. This manuscript clearly demonstrates the financial benefits of value-added product formation, such as hydrogen peroxide, over O2 formation. In a broader context, our analysis verifies that further research on valuable commodity chemicals at the anode in water splitting and CO2 reduction should be stimulated in the future to facilitate implementation of emerging, cost-intensive technologies.

Cocatalysts for Selective Photoreduction of CO2 into Solar Fuels.

Abstract: Photoreduction of CO2 into sustainable and green solar fuels is generally believed to be an appealing solution to simultaneously overcome both environmental problems and energy crisis. The low selectivity of challenging multi-electron CO2 photoreduction reactions makes it one of the holy grails in heterogeneous photocatalysis. This Review highlights the important roles of cocatalysts in selective photocatalytic CO2 reduction into solar fuels using semiconductor catalysts. A special emphasis in this review is placed on the key role, design considerations and modification strategies of cocatalysts for CO2 photoreduction. Various cocatalysts, such as the biomimetic, metal-based, metal-free, and multifunctional ones, and their selectivity for CO2 photoreduction are summarized and discussed, along with the recent advances in this area. This Review provides useful information for the design of highly selective cocatalysts for photo(electro)reduction and electroreduction of CO2 and complements the existing reviews on various semiconductor photocatalysts.

Methods, Mechanism, and Applications of Photodeposition in Photocatalysis: A Review.

Abstract: In this review, for a variety of metals and semiconductors, an attempt is made to generalize observations in the literature on the effect of process conditions applied during photodeposition on (i) particle size distributions, (ii) oxidation states of the metals obtained, and (iii) consequences for photocatalytic activities. Process parameters include presence or absence of (organic) sacrificial agents, applied pH, presence or absence of an air/inert atmosphere, metal precursor type and concentration, and temperature. Most intensively reviewed are studies concerning (i) TiO2; (ii) ZnO, focusing on Ag deposition; (iii) WO3, with a strong emphasis on the photodeposition of Pt; and (iv) CdS, again with a focus on deposition of Pt. Furthermore, a detailed overview is given of achievements in structure-directed photodeposition, which could ultimately be employed to obtain highly effective photocatalytic materials. Finally, we provide suggestions for improvements in description of the photodeposition methods applied when included in scientific papers.

Photocatalytic hydrogen production using metal doped TiO2: A review of recent advances

Abstract: Hydrogen (H2) production via photocatalytic water splitting is one of the most promising technologies for clean solar energy conversion to emerge in recent decades. The achievement of energy production from water splitting would mean that we could use water as a fuel for future energy need. Among the various photocatalytic materials, titanium dioxide (TiO2) is the dominant and most widely studied because of its exceptional physico-chemical characteristics. Surface decoration of metal/non-metal on TiO2 nanoparticles is an outstanding technique to revamp its electronic properties and enrich the H2 production efficiency. Metal dopants play a vital role in separation of electron-hole pairs on the TiO2 surface during UV/visible/simulated solar light irradiation. In this paper, the basic principles, photocatalytic-reactor design, kinetics, key findings, and the mechanism of metal-doped TiO2 are comprehensively reviewed. We found that Langmuir-Hinshelwood kinetic model is commonly employed by the researchers to demonstrate the rate of H2 production. Copper (Cu), gold (Au) and platinum (Pt) are the most widely studied dopants for TiO2, owing to their superior work function. The metal dopants can amplify the H2 production efficiency of TiO2 through Schottky barrier formation, surface plasmon resonance (SPR), generation of gap states by interaction with TiO2 VB states. The recent advances and important consequences of 2D materials, perovskites, and other novel photocatalysts for H2 generation have also been reviewed.

CO2 Reduction: From the Electrochemical to Photochemical Approach

Abstract: Increasing CO2 concentration in the atmosphere is believed to have a profound impact on the global climate. To reverse the impact would necessitate not only curbing the reliance on fossil fuels but also developing effective strategies capture and utilize CO2 from the atmosphere. Among several available strategies, CO2 reduction via the electrochemical or photochemical approach is particularly attractive since the required energy input can be potentially supplied from renewable sources such as solar energy. In this Review, an overview on these two different but inherently connected approaches is provided and recent progress on the development, engineering, and understanding of CO2 reduction electrocatalysts and photocatalysts is summarized. First, the basic principles that govern electrocatalytic or photocatalytic CO2 reduction and their important performance metrics are discussed. Then, a detailed discussion on different CO2 reduction electrocatalysts and photocatalysts as well as their generally designing strategies is provided. At the end of this Review, perspectives on the opportunities and possible directions for future development of this field are presented.

Photocatalytic fixation of nitrogen to ammonia: state-of-the-art advancements and future prospects

Abstract: The burgeoning development of ammonia (NH3) synthesis technology addresses the urgency of food intake required to sustain the population growth of the last 100 years. To date, NH3 has mostly been synthesized by the Haber–Bosch process in industry. Under the ever-increasing pressure of the fossil fuel depletion crisis and anthropogenic global climate change with continuous CO2 emission in the 21st century, research targeting the synthesis of NH3 under mild conditions in a sustainable and environment friendly manner is vigorous and thriving. Therefore, the focus of this review is the state-of-the-art engineering of efficient photocatalysts for dinitrogen (N2) fixation toward NH3 synthesis. Strenuous efforts have been devoted to modifying the intrinsic properties of semiconductors (i.e. poor electron transport, rapid electron–hole recombination and sluggish reaction kinetics), including nanoarchitecture design, crystal facet engineering, doping and heterostructuring. Herein, this review provides insights into the most recent advancements in understanding the charge carrier kinetics of photocatalysts with respect to charge transfer, migration and separation, which are of fundamental significance to photocatalytic N2 fixation. Subsequently, the challenges, outlooks and future prospects at the forefront of this research platform are presented. As such, it is anticipated that this review will shed new light on photocatalytic N2 fixation and NH3 synthesis and will also provide a blueprint for further investigations and momentous breakthroughs in next-generation catalyst design.