Cheng-Hao Chuang

The oxygen evolution reaction underpins many energy conversion technologies, yet its performance is fundamentally constrained by sluggish reaction kinetics at catalyst surfaces. Current catalyst design remains largely empirical because most strategies correlate bulk structural descriptors with overall activity rather than resolving the intrinsic kinetics of elementary reaction steps. Here, we show that open-circuit voltage–pulse voltammetry can quantitatively determine the ^* OOH formation rate, a rate-determining step in oxygen evolution. Unlike conventional electrochemical techniques, this method isolates ^* OOH formation-related electron transfer by interrupting electron transfer from electrocatalyst to external circuit while sustaining electron supply from hydroxide ions. Coupling this descriptor with a pulse voltammetry method for quantifying ^* OH deprotonation kinetics yields a unified, step-resolved kinetic framework that reveals how different dopants selectively accelerate either ^* OOH formation or ^* OH deprotonation. Fe primarily facilitates ^* OOH formation, whereas Mn selectively promotes ^* OH deprotonation. Guided by these insights, a rationally designed NiFeMn catalyst concurrently enhances both processes, delivering improved oxygen evolution performance. This methodology provides a practical means to quantify elementary reaction kinetics and accelerate the discovery of high-performance electrocatalysts.

The chlor-alkali process plays an irreplaceable role in global chemical industry, but relies heavily on RuO₂ (or IrO₂)/TiO₂-based dimensionally stable anodes, hindering sustainability and new applications. We report a facile oxygenation activation approach to create apt oxygen groups on commercial carbon black and carbon cloth. Our experimental and theoretical studies reveal that creation of carbonyl, cyclic ether, and carboxyl groups on the graphitic plane edges gives commercial carbon materials superb chlorine evolution reaction activity (overpotential: 204 mV at 1 A cm^-2), selectivity (average Faraday efficiency: 99.6 ± 1.3%), and stability (stable operation for 100 h at 0.5 A cm^-2), which is comparable to or better than the benchmark RuO₂ and dimensionally stable anodes.

The rational design of efficient oxygen reduction reaction (ORR) catalysts with maximized atom utilization is essential for advancing the oxygen depolarized cathode technology. Here, we report atomically dispersed Fe, P heteronuclear catalytic pairs on hierarchical porous carbon, in which the hydrogen bond between Fe, P catalytic pairs and ORR intermediates significantly enhances the adsorption/desorption kinetics and lowers the rate-determining step barrier of OH* desorption. Thus, Fe,P/HPC delivers an alkaline ORR performance with a half-wave potential (E_1/2) of 0.92 V and retains ∼90% of the initial activity even after 150 h operation. In addition, Fe,P/HPC achieves an E_1/2 of 0.74 V in 0.1 M HClO₄. The Fe,P/HPC-based aqueous Zn-air battery (A-ZAB) achieves a high power density of 262 mW cm^-2 and exhibits enhanced stability, sustaining a minimal voltage gap over 2800 h of constant-current cycling. Moreover, the quasi-solid-state Zn-air battery (QSS-ZAB) delivers a large open-circuit voltage of 1.52 V, while maintaining a cycling stability for over 95 h at 0.5, 1, and 2 mA cm^-2, respectively. In the chlor-alkali process, the Fe,P/HPC||RuO₂ electrolyzer enables a large current density of 300 mA cm^-2 at 1.66 V and maintains stability over 110 h. The present work pioneers the designing and construction of atomic-level heteronuclear catalysts for practical and durable cathode.

Our electrochemical approach to fabricating two-dimensional flakes and creating ordered stacks of hexagonal BN (hBN) primarily enhances the synthesis flexibility and expands their applications in the aqueous phase. Using a simple cyclic voltammetry (CV) method, freestanding hBN membranes can be formed on the Au mesh with varying structural conditions and degrees of oxidation. Raman and photoluminescence analyses confirm the high quality and distinct characteristics of the CV hBN membranes, which feature a consistent lattice structure and proper B–N bonding coordination, as in the conventional drop-cast (DC) membranes. At the atomic scale, transmission electron microscopy confirms the presence of a perfect hBN lattice structure for both DC and CV methods. However, the electron diffraction patterns reveal a difference in the number of hexagonal phases: three sets for DC hBN and two sets for CV hBN. Beyond the lattice structure, the nanoscale images from scanning transmission x-ray microscopy highlight the regions of interest and their electronic structures at the B, N, and O K-edge absorptions. Chemical bonds involving oxygen at the N and B sites occur at edges or planar surfaces as a result of the liquid process and electrochemical utilization. The DC hBN shows inequality in lattice structure and mixing stacking due to orbital correlations probed at B and N sites and variation in chemical structure owing to surface oxidation, including tri-coordinated N–O, N=O, and OH bonds. Interestingly, the CV method enhances ordered lattice symmetry and stacking structures, inducing the following N lone pairs and B–O(H) bonds in the chemical structure coordination. The use of CV in insulator hBN membranes provides an alternative approach for growing large-scale membranes, presenting new opportunities for semiconductor devices, catalytic applications, and quantum materials.

Transition-metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS₂), have emerged as a generation of nonprecious catalysts for the hydrogen evolution reaction (HER), largely due to their theoretical hydrogen adsorption energy close to that of platinum. However, efforts to activate the basal planes of TMDs have primarily centered around strategies such as introducing numerous atomic vacancies, creating vacancy-heteroatom complexes, or applying significant strain, especially for acidic media. These approaches, while potentially effective, present substantial challenges in practical large-scale deployment. Here, we report a gap-state engineering strategy for the controlled activation of S atom in MoS₂ basal planes through metal single-atom doping, effectively tackling both efficiency and stability challenges in alkaline water and seawater splitting. A versatile synthetic methodology allows for the fabrication of a series of single-metal atom-doped MoS₂ materials (M₁/MoS₂), featuring widely tunable densities with each dopant replacing a Mo site. Among these (Mn₁, Fe₁, Co₁, and Ni₁), Co₁/MoS₂ demonstrates outstanding HER performance in both alkaline and seawater alkaline media, with overpotentials at a mere 159 and 164 mV at 100 mA cm^-2, and Tafel slopes at 41 and 45 mV dec^-1, respectively, which surpasses all reported TMD-based nonprecious materials and benchmark Pt/C catalysts in HER efficiency and stability during seawater splitting, which can be attributed to an optimal gap-state modulation associated with sulfur atoms. Experimental data correlating doping density and dopant identity with HER performance, in conjunction with theoretical calculations, also reveal a descriptor linked to near-Fermi gap state modulation, corroborated by the observed increase in unoccupied S 3p states.

With the increasing demand for sustainable energy, any possibility to substitute fossil fuels becomes the key melody in the next generation of technologies. Hydrogen or oxygen evolution reaction (HER or OER) over metal oxides are thought to own the promising power capability. It becomes crucial in the advanced electrode materials for good catalytic performance, which is unclear in the reaction mechanism and catalytic optimization. Non-noble materials, such as transition metal oxide, have been heightened because of some reasons: (a) abundant hydroxyl groups on the surface, (b) size-diminished metal crystal, (c) anti-corrosion resistance in the alkaline solution. On the other hand, graphene sheet is considered one of the important 2D materials due to their unique electric transfer properties and thinnest thickness. The ability to grow functional nanomaterials on top of a graphene substrate has been proposed due to the ideal single-atom thickness, excellent electrical conductivity, transparent electrode, flexible nanosheet, and stable structure of graphene-based materials. Cobalt oxides, as one of the active electrocatalysts, have been proven to be one class of HER/OER in an alkaline environment. The facial functional groups (hydroxyl, carboxyl, and epoxide) of nanocomposite synthesis are characteristic for the interesting interaction with metal site. ^{[ 1]} By the strong covalent bonding between O and Co, the oxidation state of Co ³⁺ in Co ₃O ₄ can be partially reduced to Co ²⁺ state among individual Co ₃O ₄ nanocrystal/graphene. ^{[ 2]} Since the nano-scaled microscopic probing is still absent for the detail and direct observation, we will demonstrate the element-specific chemical images to promote the graphene-related electrode for the future liquid-cell applications.

Advancements in single-atom-based catalysts are crucial for enhancing oxygen evolution reaction (OER) performance while reducing precious metal usage. A comprehensive understanding of underlying mechanisms will expedite this progress further. Here we report Ir single atoms coordinated out-of-plane with dimethylimidazole (MI) on CoFe hydroxide (Ir₁/(Co,Fe)-OH/MI). This Ir₁/(Co,Fe)-OH/MI catalyst, which was prepared using a simple immersion method, delivers ultralow overpotentials of 179 mV at a current density of 10 mA cm⁻² and 257 mV at 600 mA cm⁻² as well as an ultra-small Tafel slope of 24 mV dec⁻¹. Furthermore, Ir₁/(Co,Fe)-OH/MI has a total mass activity exceeding that of commercial IrO₂ by a factor of 58.4. Ab initio simulations indicate that the coordination of MI leads to electron redistribution around the Ir sites. This causes a positive shift in the d-band centre at adjacent Ir and Co sites, facilitating an optimal energy pathway for OER.

The oxygen evolution reaction (OER) provides the protons for many electrocatalytic power-to-X processes, such as the production of green hydrogen from water or methanol from CO₂. Iridium oxohydroxides (IOHs) are outstanding catalysts for this reaction because they strike a unique balance between activity and stability in acidic electrolytes. Within IOHs, this balance varies with the atomic structure. While amorphous IOHs perform best, they are least stable. The opposite is true for their crystalline counterparts. These rules-of-thumb are used to reduce the loading of scarce IOH catalysts and retain the performance. However, it is not fully understood how activity and stability are related at the atomic level, hampering rational design. Herein, we provide simple design rules (Figure 12) derived from the literature and various IOHs within this study. We chose crystalline IrOOH nanosheets as our lead material because they provide excellent catalyst utilization and a predictable structure. We found that IrOOH signals the chemical stability of crystalline IOHs while surpassing the activity of amorphous IOHs. Their dense bonding network of pyramidal trivalent oxygens (μ_3Δ-O) provides structural integrity, while allowing reversible reduction to an electronically gapped state that diminishes the destructive effect of reductive potentials. The reactivity originates from coordinative unsaturated edge sites with radical character, i.e., μ₁-O oxyls. By comparing to other IOHs and literature, we generalized our findings and synthesized a set of simple rules that allow prediction of stability and reactivity of IOHs from atomistic models. We hope that these rules will inspire atomic design strategies for future OER catalysts.