Dr Cui Ying Toe

Photoelectrochemical oxidation (PECO) is a promising advanced technology for treating micropollutants in stormwater. However, it is important to understand its operation prior to practical validation. In this study, we introduced a flow PECO system designed to evaluate its potential for full-scale applications in herbicides degradation, providing valuable insights for future large-scale implementations. The PECO flow reactor demonstrated the ability to treat a larger volume of stormwater (675 mL, approximately 10 times more than previous batch experiments) with effective removal rates of 92 % for diuron and 22 % for atrazine over 6 h of operation at 2 V. To address the large volume issue in stormwater treatment, a multiple module parallel application design is being considered to increase the treatment capacity of the PECO flow reactor. During the flow reactor operations, flow rate was found to have a notable impact on removal performance, particularly for diuron. At a flow rate of 610 mL min-1, approximately 90 % removal of diuron was achieved, while at 29 mL min-1, the removal efficiency decreased to 60 %. While light intensity had minimal effect on diuron degradation (all settings achieved over 90 % removal), it enhanced atrazine degradation from 9 % to 31 % with an increase in intensity from 63 mW cm-2 to 144 mW cm-2. Remarkably, the PECO flow system exhibited excellent removal performance (>90 % removal) for diuron even at extremely high initial pollutant concentrations (240 µg L-1), demonstrating its capacity to handle varying contaminant loads in stormwater. Energy consumption analysis revealed that flow rate as the primary factor influenced the specific energy consumption rate. Higher flow rate (e.g., 610 mL min-1) were preferable in flow reactor due to its well-balanced performance between removal and energy consumption. These findings confirm that the PECO flow system offers an efficient and promising approach for stormwater treatment applications.

Accurate band-gap prediction is essential for designing and discovering new materials with desired properties. However, current methods for calculating band gaps based on local and semilocal functionals lead to significant underestimation, hindering the effectiveness of in silico and high-throughput screening of materials. We present a machine learning model with domain adaptation to rapidly yield accurate band-gap prediction of semiconductors (oxides, chalcogenides, nitrides, phosphides, etc.). The approach circumvents the prerequisite for a large amount of physically measured band-gap data, which is notoriously scarce. It instead sources knowledge from a large dataset with underestimated band gaps and subsequently transfers knowledge to train a crystal graph convolution neural network (CGCNN) using a small dataset of accurate, physically measured band gaps. The prediction model shows a low mean absolute error (MAE) of 0.23 eV, outperforming those using Perdew-Burke-Ernzerhof (PBE) functionals (MAE = 0.87 eV). Visualization of the learned crystal graph using the t-distributed stochastic neighbor embedding (t-SNE) algorithm revealed that the crystal structure and composition have a strong influence on the material band gaps.

Solar water splitting by means of photoelectrochemical (PEC) cells offers the promise to produce cost-effective renewable and clean fuel from abundant sunlight and water. Lately, the realization of promise of concurrent hydrogen (H2) production along with alternate oxidation reaction (which is less energetically demanding than the water oxidation reaction) has also become a subject of intense global research interests. At present, developing inexpensive, non-toxic, and earth-abundant semiconductor-based photoelectrodes (i.e. photocathode and photoanode) with a high stability is of great importance in achieving economically viable H2 production and value-added chemicals. This review summarizes recent advances in these photoelectrodes along with contemporary understanding of key factors responsible for high solar-to-hydrogen efficiency, device stability, and highlights a promising new research trend of alternate oxidation reactions at photoanodes. First, we outline recent developments of novel photoelectrode materials using high-throughput computational screening integrated with ab-initio calculations. We proceed to discuss the merits and major challenges of these novel and existing photoelectrodes and links the strategies used to overcome these challenges to achieve economically viable solar H2 generation. Several important studies on the emerging new trend of alternate oxidations reactions at photoanodes toward value-added chemicals are then detailed with particular emphasis is placed on dependency of photoanode design on type of organic feedstocks and desired products from the oxidation reaction. We also emphasize the development of tandem devices for overall water splitting using these photoelectrodes with high onset potentials. Finally, we provide not only promising future directions for each material system, but also a critical assessment and outlook on how these earth-abundant photoelectrodes could lead to a potential large-scale implementation of water splitting devices.

Exploring advanced technologies to efficiently produce green hydrogen energy is imperative to alleviate the energy crisis and environmental pollution. Conventional overall water electrolysis (OWE) has been regarded as a promising approach for effective H2 production, however, it is largely restricted by the sluggish kinetics of the anodic oxygen evolution reaction (OER). Coupling kinetically favorable anodic reactions, such as biomass-derived compound oxidation and pollutant degradation, with the hydrogen evolution reaction (HER) in hybrid water electrolysis (HWE), can not only solve the biomass recycling and pollutant emission problems but also save the energy cost for clean H2 generation. Hence, various advanced earth-abundant electrocatalysts have been developed to catalyze those promising anodic reactions, yet some problems such as tedious preparation and unsatisfactory performance still exist. Given the gap between research and practical applications, this review summarizes the recent progress in electrocatalysts for diverse alternative anodic oxidation reactions over the last five years together with their application in HWE systems. An in-depth understanding of different reaction mechanisms and assessments toward electrocatalysts is discussed to further enhance anodic efficiency. The advantages, differences, and critical issues of different HWE systems are thoroughly discussed as well, providing a new avenue for low-voltage H2 production from renewable resources and waste products.

Graphene edges exhibit a highly localized density of states that result in increased reactivity compared to its basal plane. However, exploiting this increased reactivity to anchor and tune the electronic states of single atom catalysts (SACs) remains elusive. To investigate this, a method to anchor Pt SACs with ultra-low mass loadings at the edges of edge-rich vertically aligned graphene (as low as 0.71¿µg¿Pt¿cm¿2) is developed. Angle-dependent X-ray absorption spectroscopy and density-functional theory calculations reveal that edge-anchored Pt SACs has a robust coupling with the p-electrons of graphene. This interaction results in a higher occupancy of the Pt 5d orbital, shifting the d-band center toward the Fermi level, improving the adsorption of *H for the hydrogen evolution reaction (HER). Pt primarily coordinated to the graphene edge shows improved alkaline HER performance compared to Pt coordinated in mixed environments (turnover frequencies of 22.6 and 10.9¿s¿1 at an overpotential of 150¿mV, respectively). This work demonstrates an effective route to engineering the coordination environment of Pt SACs by using the graphene edge for enhanced energy conversion reactions.

The intrinsic carrier dynamics of cuprous oxide (Cu2O) are known to have a crucial influence on photocatalytic performances. The photoactivity of rhombic dodecahedral Cu2O with dominant {110} facets (RD-Cu2O) is demonstrated to surpass that of cubic Cu2O with {100} surfaces (CB-Cu2O). Time resolved microwave conductivity (TRMC) measurements reveal the higher carrier mobility of RD-Cu2O when compared to CB-Cu2O. Additionally, modulated surface photovoltage (SPV) measurements further supported the better charge separation efficiency of RD-Cu2O. Although CB-Cu2O exhibited more pronounce SPV signals, the homogeneous distribution of electrical fields drives the majority charge inward and led to detrimental charge recombination. In contrast, the weak SPV signals for RD-Cu2O were attributed to a modulated distribution of charges towards the facets and facet boundaries, demonstrating a better charge separation. This study shows that carrier dynamics and defect density should also be regarded as facet-dependent properties that can have deciding influence on the photocatalytic activity. This journal is

Photocatalytic and photoelectrochemical processes are two key systems in harvesting sunlight for energy and environmental applications. As both systems are employing photoactive semiconductors as the major active component, strategies have been formulated to improve the properties of the semiconductors for better performances. However, requirements to yield excellent performances are different in these two distinctive systems. Although there are universal strategies applicable to improve the performance of photoactive semiconductors, similarities and differences exist when the semiconductors are to be used differently. Here, considerations on selected typical factors governing the performances in photocatalytic and photoelectrochemical systems, even though the same type of semiconductor is used, are provided. Understanding of the underlying mechanisms in relation to their photoactivities is of fundamental importance for rational design of high-performing photoactive materials, which may serve as a general guideline for the fabrication of good photocatalysts or photoelectrodes toward sustainable solar fuel generation.