Friday, January 30, 2026

How topological surfaces boost clean energy catalysts

Advanced Institute for Materials Research (AIMR), Tohoku University

image:
Identification of the electrochemical surface state (ESS) of monolayer PtBi2 by a DFT-based surface Pourbaix diagram.
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Credit: Heng Liu et al.

The oxygen reduction reaction (ORR) is a key process in fuel cells and metal-air batteries, technologies expected to play a central role in a low-carbon energy future. However, ORR proceeds slowly on most materials, limiting efficiency and increasing costs. Finding catalysts that can speed up this reaction is therefore a major challenge in reducing our energy footprint.

Two-dimensional (2D) topological materials have recently attracted attention as potential electrocatalysts. Their unusual electronic properties arise from spin-orbit coupling (SOC), which creates robust topological surface states (TSSs) that can enhance charge transport. Until now, most studies have assumed these surfaces remain clean and unchanged during reactions.

But the reality is different. In real electrochemical environments catalyst surfaces are far from pristine. They constantly interact with the surrounding electrolyte and reaction intermediates, forming so-called electrochemical surface states (ESSs). Understanding how these realistic surfaces affect the topological properties and catalytic performance is necessary if scientists are to utilize 2D topological materials.

To address this issue, researchers at Tohoku University examined monolayer platinum bismuthide (PtBi₂), an atomically thin two-dimensional material, as a model topological electrocatalyst. By combining quantum-level calculations with models that capture how reactions depend on pH, the team determined the catalyst's true working surface under oxygen reduction conditions.

Their results revealed that PtBi₂ is stabilized at ORR-relevant potentials with nearly one monolayer of hydroxyl (HO*) species covering its surface. This means the active surface is not the idealized topological surface, but an HO*-induced electrochemical surface state formed during operation.

Importantly, this surface reconstruction does not erase the material's topological nature. Instead, it reshapes the electronic landscape, creating localized SOC-enabled surface states and a flat-band-like feature with a high density of electronic states near the Fermi level. These features enhance electronic coupling to ORR intermediates and reduce sensitivity to interfacial dipoles.

Much like roads can guide crowded traffic, the topological framework steers electron flow in beneficial ways despite adsorbates covering the catalyst surface.

By explicitly accounting for pH effects, the researchers further predict that PtBi₂ achieves near-peak ORR activity in alkaline environments. This highlights the importance of evaluating catalytic performance under realistic electrochemical conditions rather than relying on idealized surface models.

"Our findings show that topological surface states can survive, and even be optimized by, electrochemical reconstruction," says Hao Li, a Distinguished Professor at Tohoku University's WPI-AIMR. "This provides a practical design principle for next-generation electrocatalysts, where quantum topology and electrochemical surface chemistry must be considered together."

Additionally, all the computational results have been uploaded to the Digital Catalysis Platform (DigCat), the world's first and largest experimental + computational catalysis database to date, developed by the Hao Li Lab.

Details of their findings were published in the Journal of Physical Chemistry Letters on December 9, 2025.

About the World Premier International Research Center Initiative (WPI)

The WPI program was launched in 2007 by Japan's Ministry of Education, Culture, Sports, Science and Technology (MEXT) to foster globally visible research centers boasting the highest standards and outstanding research environments. Numbering more than a dozen and operating at institutions throughout the country, these centers are given a high degree of autonomy, allowing them to engage in innovative modes of management and research. The program is administered by the Japan Society for the Promotion of Science (JSPS).

See the latest research news from the centers at the WPI News Portal: https://www.eurekalert.org/newsportal/WPI
Main WPI program site: www.jsps.go.jp/english/e-toplevel

Advanced Institute for Materials Research (AIMR)
Tohoku University
Establishing a World-Leading Research Center for Materials Science
AIMR aims to contribute to society through its actions as a world-leading research center for materials science and push the boundaries of research frontiers. To this end, the institute gathers excellent researchers in the fields of physics, chemistry, materials science, engineering, and mathematics and provides a world-class research environment.

Journal

The Journal of Physical Chemistry Letters

DOI

10.1021/acs.jpclett.5c03589

Article Title

2D Topological Electrocatalysts with Spin−Orbit Coupling: Interplay between the "Electrochemical" and "Topological" Surface States

HKUST develops breakthrough high‑efficiency, low‑cost wastewater treatment technology

Achieving 20‑fold efficiency increase and significant cost reduction of 50%

Hong Kong University of Science and Technology

image:
Prof. CHEN Guanghao (center), Chair Professor of the Department of Civil and Environmental Engineering, and his research group members in the same department, postdoctoral fellow Dr. GUO Hongxiao (left) and PhD student Mr. LUO Yu (right).
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Credit: HKUST

The Hong Kong University of Science and Technology (HKUST) research team has developed a groundbreaking wastewater treatment technology that integrates a mesh bioreactor with an ultrasound-induced transient cavitation cleaning mechanism. The system can complete mesh cleaning within 3.8 seconds under anaerobic conditions and achieves 10-20 times higher flux than conventional membrane bioreactors (MBRs). The technology operates efficiently with substantially lower energy consumption, produces treated effluent surpassing international and local discharge standards, and reduces the cost of treating each cubic metre of wastewater to 50% of conventional MBRs, offering a sustainable solution for both municipal and industrial wastewater treatment.

The research was led by Prof. CHEN Guanghao, Chair Professor of the Department of Civil and Environmental Engineering at HKUST, together with Dr. GUO Hongxiao, Postdoctoral Fellow and Mr. LUO Yu, PhD student in the same department. The study, titled “Transient cavitation enables ultrafast fouling removal in mesh bioreactors for efficient sludge–liquid separation during wastewater treatment”, was published in the journal Nature Water.

Conventional secondary wastewater treatment worldwide commonly relies on MBR systems, where aerobic or anaerobic microorganisms degrade organic matter in wastewater. Under the Hong Kong Drainage Services Department standards, the total suspended solids (TSS) of secondary-treated effluent must reach 30 mg/L or below. While MBRs are effective in separating suspended biomass from water, they face persistent membrane fouling, requiring regular cleaning and membrane replacement, leading to high operational costs.

The HKUST team designed a mesh bioreactor (MeBR) using 10-200 μm mesh material to achieve separation mainly through a biocake layer that self-forms on the mesh from retained solids and microbial biomass. The technology incorporates piezoelectric ultrasound transducers that generate cavitation of microbubbles, which rapidly form and collapse to remove fouling from the mesh surface. This mechanism enables complete cleaning within 10 seconds under aerobic conditions, and as quickly as 3.8 seconds under anaerobic conditions when treating domestic wastewater.

Key breakthroughs of the system include:

Each square metre of mesh can process 148-307 L m−2 h−1, achieving 10-20 times the flux of conventional MBRs while maintaining mesh integrity over long-term operation.
The treated effluent maintains a TSS below 20 mg/L, outperforming Hong Kong’s 30 mg/L standard and meeting discharge requirements in approximately 75% of the global population.
The system requires only 2.5-47 Wh/m³, significantly reducing overall operational expenditure.

The first author of the paper and PhD student at HKUST Mr. Luo Yu explained, "Across 120 days of continuous filtration tests and an additional 21‑day trial using real municipal wastewater, the meshes retained their structural integrity. Although minor physical changes—such as variations in pore size and surface roughness—were observed after long-term operation, they did not compromise the mechanical stability of the meshes, demonstrating the system's durability."

Dr. Guo Hongxiao, corresponding author added, "The technology enables the mesh to operate stably at ultrahigh fluxes that far exceed those of typical MeBRs and reach 10-20 times those of conventional MBR systems, without any additional cleaning requirements. The ultrahigh fluxes also reduce the biocake reformation period to under 10 minutes, overcoming a long-standing challenge and ensuring stable effluent quality during continuous operation."

Prof. Chen Guanghao, corresponding author, stated, "Cities worldwide are facing increasing pressures from climate change, rising energy costs and growing wastewater loads. Treating more wastewater with fewer resources is becoming a universal challenge. This technology demonstrates that high‑flux treatment can be achieved while still meeting stringent global discharge standards, potentially easing the burden on existing facilities and offering a more flexible solution for densely populated cities. Based on current analyses, the system can reduce the treatment cost by approximately US$0.05 per cubic metre of wastewater resulting in significant cumulative benefit. Ultimately, our goal is to deliver research that creates real and meaningful value for society."

Schematic of transient cavitation-driven biofouling control using piezoelectric device.

Credit

HKUST