How to Choose a Hydrogen Evolution (HER) Catalyst: Kinetic Barriers in Water Electrolysis, AWE/PEM/AEM Pathways, and a Materials-Family Roadmap (with a Product Map)

Why study hydrogen evolution catalysts: where is the “kinetic barrier” in water electrolysis?

Splitting water into hydrogen and oxygen is essentially converting electrical energy (or photo-generated electrical energy) into chemical bond energy. Thermodynamically, under 25 °C conditions, the reversible voltage for water splitting is about 1.23 V (corresponding to ΔG° ≈ 237 kJ/mol H₂O). But this is only the “theoretical minimum threshold.” Real systems must additionally overcome kinetic barriers and various resistive losses, so the practical operating voltage is higher.

Another commonly used reference is the thermoneutral voltage, which is about 1.48 V at 25 °C (corresponding to ΔH ≈ 285.8 kJ/mol H₂). It reflects the total energy demand under isothermal operation; in real devices, the cell voltage further includes kinetic, ohmic, and mass-transport losses.

The value of a catalyst lies in this: at the same hydrogen production rate, it drives the reaction with a lower extra voltage (overpotential), and maintains performance without significant decay during long-term operation.

What exactly happens in HER?

In acidic electrolytes, HER (Hydrogen Evolution Reaction) is commonly described by three steps:

1. Volmer (discharge/adsorption):

H₃O⁺ + e⁻ → H* + H₂O

2. Heyrovsky (electrochemical desorption):

H* + H₃O⁺ + e⁻ → H₂ + H₂O

3. Tafel (chemical recombination):

H* + H* → H₂

In alkaline/neutral media, the same three-step framework is often written as:

1. Volmer:

H₂O + e⁻ → H* + OH⁻

2. Heyrovsky:

H* + H₂O + e⁻ → H₂ + OH⁻

3. Tafel:

2H* → H₂

Here, H* denotes the “active hydrogen intermediate” adsorbed on the catalyst surface. How fast the overall reaction proceeds often depends on which step is the slowest (the rate-determining step).

Key difference: why is “alkaline HER is harder” so often mentioned?

• In alkaline media, the proton source is not H⁺ but primarily water. The Volmer step therefore requires breaking an O–H bond (“water dissociation”) before forming H*. As a result, many systems are more easily limited by the Volmer step. Many reviews and studies point out that Volmer (water dissociation) is often the main rate-limiting step in alkaline HER.
• Note: The rate-determining step can change with the catalyst material, surface coverage, and the overpotential range. Interpreting Tafel slopes or Volmer–Heyrovsky behavior is model-dependent, so you should not draw definitive conclusions from a single slope alone.

How to judge whether an HER catalyst is good: save energy, accelerate, and last

What you care about	Reframed as a question	How to judge quickly from plots	Common reasons for poor performance (key causes)
Save energy (activity)	At the same hydrogen production rate, does it need a higher voltage to “push” the reaction?	Compare at a fixed hydrogen production rate (often represented by a fixed current density in experiments). At this rate, lower required voltage is better (lower energy consumption).	Intrinsically slow active sites (unfavorable surface chemistry); charges/ions cannot reach sites effectively (poor conductivity, poor interfacial contact, thick film blockage); large resistive losses (solution/electrode/contact resistance).
Accelerate (kinetics)	If I want it to produce hydrogen faster, does the voltage need to increase sharply?	Look at how much extra voltage is needed to go from a “medium rate” to a higher rate. Smaller additional voltage is better (easier acceleration; suitable for high loading).	The rate-determining step becomes a bottleneck (often “water dissociation / O–H breaking” in alkaline media); mass transport and bubble effects grow (bubble coverage, local concentration gradients at high current); catalyst layer/electrode structure not suited for high current.
Last (stability)	Can it run continuously for a long time without obvious degradation—does it degrade gradually or fail abruptly?	After long-term operation: does it become “harder” (needs higher voltage to maintain the same rate), or does the rate drop at the same voltage? Also compare before/after curves to see whether the change is significant.	Chemical degradation (oxidation/dissolution/poisoning); structural evolution (surface reconstruction, agglomeration, phase change); mechanical/interfacial failure (catalyst layer delamination, binder issues, unstable support/interface).

One-sentence summary: a good catalyst = more energy-efficient + easier to accelerate + more durable.

Common paper metrics: a quick glossary

Goal	Common notation in papers	What it actually means
Save energy (activity)	η@10 mA·cm⁻² (or η@100, etc.)	The extra voltage (overpotential) required at a fixed current density (fixed hydrogen production rate). Smaller values mean better energy efficiency. (Note: for half-cells, smaller η (vs RHE) is better; for full cells, smaller Vcell is better.)
Accelerate (kinetics)	Tafel slope (mV/dec)	How many mV of overpotential are needed to increase current (hydrogen production rate) by 10×—often understood as the “cost of acceleration.”
Last (stability)	CP/CA stability curves + polarization curves before/after	Whether performance decays during long runs and how severe it is; comparing polarization curves before and after helps confirm whether performance truly degraded.

Note: The Tafel slope depends on the fitting window, iR compensation, surface coverage, and mechanistic assumptions. It is best treated as a kinetic descriptor, not a standalone mechanistic proof. Ideally, interpret it together with EIS, exchange current density / near-onset behavior, etc.

In a real electrolyzer, where does the “voltage” go?

You can think of the total cell voltage as three parts:

1. Thermodynamic voltage: ideally about 1.23 V at 25 °C (the “theoretical minimum threshold”).
2. Kinetic losses: both cathodic HER and anodic OER require extra driving force (overpotentials).
3. Ohmic and transport losses: membrane/diaphragm, electrolyte, electrode/interfacial resistances, plus additional losses from bubbles and mass transport.

So, the practical meaning of “a good HER catalyst” is very concrete: at the same hydrogen production rate, it makes the cathode consume less voltage, and at high current density it is not dragged down by transport, bubbles, or interface problems.

That is, the total voltage can be written as:

• Vcell = 1.23 V (thermodynamic floor) + ηHER (cathode kinetics) + ηOER (anode kinetics) + iR (ohmic losses: membrane/diaphragm, electrolyte, contacts) + transport/bubble losses (more pronounced at high current)

Three mainstream water-electrolysis pathways

Pathway	Main ion conduction / medium	Cathode environment	Most common “hard constraints” in selection	Main focus for cathode catalyst selection
AWE (traditional alkaline water electrolysis)	Liquid alkali (KOH/NaOH) + diaphragm	Alkaline	Mature engineering; scalable; bubble and transport limitations become significant at high current	Acceleration + durability first (electrode structure, bubble release, bonding/adhesion); activity matters but is often overshadowed by “structure/transport.”
PEMWE (proton exchange membrane water electrolysis)	Acidic membrane (proton-conducting)	Acidic (more stringent for materials)	High corrosion/dissolution risk; strong materials constraints	Energy saving first (low overpotential, high efficiency), while also ensuring durability; cathode often uses Pt as the most reliable route or benchmark.
AEMWE (anion exchange membrane water electrolysis)	Alkaline membrane (anion-conducting)	Alkaline (but in a membrane–electrode architecture)	Durability of membrane/ionomer and interfaces; water management and transport	Acceleration + durability are critical (ion pathways + interfacial resistance + water/bubble management); materials and electrode engineering must be chosen together.

Materials-family roadmap: how to classify common HER catalysts—strengths, weaknesses, and typical levers

Family	More common / more advantageous environment	Strengths	Common weaknesses	Typical improvement levers
Noble metals: Pt / Pt/C	Acidic (especially PEM cathode benchmarks / common in engineering)	Very energy-efficient; smooth kinetics; most reliable benchmark	Cost and resource constraints; at high load, support and interface still matter	Lower loading (higher utilization), better supports/electrode structures, lower interfacial resistance
Ni-based (Ni, Ni alloys, NiMo, etc.)	Alkaline (mainline for AWE/AEM cathodes)	Engineering-friendly; can balance efficiency and durability in alkaline; scalable	At high current, easily limited by transport/bubbles/interfaces; long-term structural/interfacial changes	Self-supporting electrodes (Ni foam, etc.), alloying/composites, pore-structure optimization and binder/ion-channel tuning
Transition-metal sulfides (e.g., MoS₂)	Common in research (acidic/alkaline; highlights structure–property relationships)	Great “teaching case” for active-site engineering	Conductivity, interfaces, and long-term stability often bottlenecks; scale-up at high current relies on electrode engineering	Phase/defect/doping to improve conductivity and site quality; compositing with conductive frameworks; stabilization (suppress oxidation/dissolution)
Phosphides (Ni₂P/CoP, etc.)	Common in alkaline and AEM research	Good conductivity; often accelerates well	Long-term chemical stability and surface reconstruction must be verified	Composite and interfacial engineering, protective/stabilizing phases, electrode-structure optimization
Carbides / nitrides (Mo₂C, VN, etc.)	Often used for composites/synergy	High conductivity; can serve as frameworks or synergistic sites	Durability under real operating conditions is highly interface-dependent	Composite with active phases, surface stabilization, pore-channel and binder optimization

Summary:

1. For acidic/PEM cathodes, using Pt as the benchmark “ruler” is the safest starting point.
2. For alkaline AWE/AEM cathodes, Ni-based systems (especially NiMo and self-supporting electrode concepts) are the most common and most engineering-relevant.
3. Other families are often routes with performance potential, but still require electrode engineering and durability validation for practical deployment.

Common product forms and a practical selection workflow

Common product categories

Category	Typical examples	Mainly affects which “thing”	The 3 most important points to check/ask
Finished catalysts (powders/slurries)	Pt/C, Ni-based powders, MoS₂/phosphide powders, etc.	Mainly energy saving, also affects acceleration	① Acid/alkali compatibility ② Conductivity/interface friendliness ③ Whether a stable catalyst layer can be formed
Electrodes/supports (structure governs high-current performance)	Ni foam, carbon paper/carbon cloth, metal meshes, etc.	Acceleration + durability (most critical)	① Pore structure / bubble release ② Conductivity and contact ③ Corrosion resistance and adhesion
Precursors/raw chemicals (for synthesis/in situ growth)	Metal salts (Ni/Co/Mo, etc.), sulfur/phosphorus sources	Energy saving + durability (determines phase/defects/doping)	① Controllability of target phase/composition ② Impact of impurities/water ③ Heat-treatment/growth window
Film and interface additives	Ionomers/binders, solvents, dispersants	Acceleration + durability (often overlooked)	① Sufficient ion pathways ② Whether interfacial resistance is introduced ③ Reliable drying/adhesion
Electrolytes and reference systems	KOH/NaOH or acids; benchmark catalysts	All three (environment defines the bottleneck)	① Acid/alkali match ② Consistent concentration/purity ③ Validate test credibility using reference samples

Selection Workflow

① First, define the device / medium

1. PEM (acidic membrane) → for the cathode, start with Pt-based catalysts as the benchmark / engineering baseline
2. AWE/AEM (alkaline) → for the cathode, start with Ni-based catalysts (including NiMo / self-supported electrode concepts)

② Next, define the target “hydrogen output intensity” (current-density range)

1. Low / medium current: focus more on intrinsic material activity (energy saving)
2. High current: focus more on electrode structure / transport / bubbles (rate capability + durability)

③ Choose the catalyst family (start with the “environment-compatible backbone”)

1. Acidic: Pt (reference / mainline route) → then consider lowering noble-metal content and structural optimization
2. Alkaline: Ni-based mainline → then consider sulfides / phosphides, etc. as expansion options

④ Choose the “form factor” route (sets reproducibility and high-current behavior)

1. Powder-coated electrodes: versatile, easy to benchmark
2. In situ grown / self-supported electrodes: higher potential at high current
3. Composite electrodes: system design of conductive framework + active phase + ion-transport pathways

⑤ Don’t overlook the supporting components (many “underperformance / poor durability” root causes are here)

1. Support/substrate, binder/ionomer, solvent & dispersion, drying process

⑥  Verify with the “energy saving – rate capability – durability” checklist

1. Energy saving: is the voltage low enough at a fixed rate?
2. Rate capability: does it stay smooth at higher rates, or does it fall behind?
3. Durability: long-term decay + before/after comparisons—are the changes significant?

HER (Hydrogen Evolution Reaction) Catalyst R&D Selection “Product Map”: Catalyst Materials / Precursors / Electrolytes & Buffers / Electrode-Building Materials / Solvents & Additives — Category Navigation + Representative Product Tables

Selection Navigation Table

Theme Table	When should you look at this table first?	What’s inside	Quick selection tips
Table A — Catalyst materials & benchmark references	When you want to test HER directly: activity screening, reproducibility checks, benchmarking vs literature/peers	Pt black benchmark; MoS₂/WS₂; Ni/Co/Fe sulfides; NiP/CoP; Mo₂C; VN, etc.	Run Pt black first to establish a “baseline.” Then choose sulfides/phosphides/carbides/nitrides for family comparisons, paying attention to particle size and whether conductive compositing is needed.
Table B — Metal salts / single-source precursors	When you will synthesize, support-load, or electrodeposit catalysts (Ni/Co/Mo/W/Pt systems, etc.)	Soluble Ni/Co/Mo/W precursors; Mo–S single-source precursor; Pt(IV)/Pt(II) precursors	For “reproducible synthesis,” prioritize high-purity precursors (e.g., PrimorTrace™ Ni salts). Choose Pt precursors based on oxidation state and reduction kinetics.
Table C — Conversion/doping reagents & additives	When you need sulfidation/phosphidation/N-doping/reductive deposition/morphology control	S sources (thiourea/thioacetamide/Na₂S/thiosulfate); P sources (hypophosphites); N sources (urea/melamine); NaBH₄; citric acid/EDTA; SDS/CTAB/PVP	Match the synthesis route to the “reaction mechanism”: slow-release sulfur sources (thioacetamide/thiourea) often favor morphology control; NaBH₄ enables fast reduction; surfactants/polymers require thorough washing and blank controls.
Table D — Electrolytes / buffers / supporting salts	When preparing electrolytes or running anion-effect / neutral-media controls	Strong acids (H₂SO₄/HClO₄/HCl); strong bases (KOH/NaOH); supporting salts (KCl/sulfates); phosphate buffers; borate systems	To minimize specific adsorption: in acidic tests, consider HClO₄ as a reference. For neutral/buffered systems, a three-way comparison (phosphate vs borate vs sulfate) is often the clearest.
Table E — Electrode-building materials	When making catalyst inks, coatings, GDEs, or membrane electrodes	PVDF/PTFE binders; Nafion membrane; conductive carbon black; functionalized graphene supports	Decide the platform first: alkaline powder electrodes often use PVDF + NMP; acidic/PEM systems use Nafion membranes (often with Nafion ionomer); for conductive networks, prioritize carbon black.
Table F — Solvents & cleaning	When cleaning electrodes, preparing inks, or controlling residual solvent	High-purity water; IPA/ethanol; NMP; ethylene glycol	Use IPA/ethanol + high-purity water for cleaning. For films, key is consistent solvent evaporation and residual solvent control (high-boiling solvents like NMP/ethylene glycol require stricter drying control).

A. Catalyst Materials & Benchmark References (Direct HER Testing)

Category	CAS No.	Aladdin Cat. No.	Name	Spec / Purity	Product features / role (HER-related)
HER benchmark catalyst / reference	7440-06-4	P433438	Platinum black, 98+	For analysis, premium grade, ≥98%	A classic “gold-standard” HER activity reference (used to verify whether the system, electrode fabrication, and test workflow are reliable); also useful for small-dose blending to boost activity as a comparison.
HER catalyst (MoS₂)	1317-33-5	M476416	Molybdenum disulfide	Dispersion, 0.1–0.5 mg/mL in H₂O	Ready-to-use MoS₂ dispersion for rapid “material screening/electrode coating”; HER activity often correlates with edge sites/defects/phase and conductive compositing.
HER catalyst / precursor (WS₂)	12138-09-9	T431601	Tungsten(IV) sulfide	≥99.995% metals basis, crystal	High-purity crystalline WS₂ for HER fundamental studies/benchmarking or as a composite precursor; stability and conductive compositing are often key.
HER catalyst / precursor (CoSₓ)	12013-10-4	C475140	Cobalt sulfide	≥99.98% metals basis	Cobalt sulfides can be used directly as HER catalysts or as precursors for further conversion (phosphidation/nitridation/carbon coating, etc.); surface reconstruction may occur electrochemically.
HER catalyst / precursor (NiSₓ)	16812-54-7	N283361	Nickel sulfide	≥99.9% metals basis	A typical non-noble HER candidate; also commonly used as a precursor for further conversion (phosphidation/nitridation/carbon coating, etc.).
HER catalyst / precursor (NiSₓ, different particle size)	12035-72-2	N475047	Nickel sulfide	≥99.7% metals basis, >150 mesh	Same NiSₓ family as above, but particle size/surface area and film-forming behavior may differ; more suitable for pellet pressing/filling or particle-size comparison.
HER catalyst / precursor (FeSₓ)	12068-85-8	I302622	Iron sulfide	≥99.9% metals basis	Can serve as (or contribute to) catalytic/synergistic components in sulfide systems; corrosion resistance and stability must be evaluated carefully under certain conditions.
HER catalyst (phosphide)	12134-02-0	C336121	Cobalt phosphide	≥99.9% metals basis	CoP is a classic alkaline HER family (high conductivity, rich active sites); often undergoes surface reconstruction in practice and should be assessed under the chosen electrolyte conditions.
HER catalyst (phosphide)	12035-64-2	N466325	Nickel phosphide	≥98%, −100 mesh	NiPₓ (common families include Ni₂P/Ni₅P₄, etc.) is widely used for alkaline HER; particle size affects ink dispersion and coating densification.
HER catalyst (carbide)	12069-89-5	M302624	Molybdenum carbide	≥99.95% metals basis	Mo₂C materials are highly conductive and can act as HER catalysts or supports; often composited with carbon/sulfides/phosphides to improve stability and activity.
HER catalyst / conductive support (nitride)	24646-85-3	V303188	Vanadium nitride (VN)	≥99.9% metals basis	Conductive nitride that can be used as an HER catalyst or composite support; the surface may readily form oxide/hydroxide layers, so interface tuning via activation or compositing is often used.

B. Metal Salts / Single-Source Precursors (For Synthesis, Loading, Deposition)

Category	CAS No.	Aladdin Cat. No.	Name	Spec / Purity	Product features / role (HER-related)
Pt precursor (electrodeposition / loading)	18497-13-7	C755674	Chloroplatinic acid hexahydrate	BioReagent	A commonly used Pt(IV) precursor for preparing supported Pt nanoparticles (Pt/C, Pt/oxides, etc.), chemical reduction, or electrodeposition; used for Pt reference electrodes/calibration.
Pt precursor (Pt(II))	10025-99-7	P128374	Potassium tetrachloroplatinate(II)	≥99.9% metals basis, Pt ≥46%	Pt(II) precursor suitable for Pt loading/coordination routes or controlling reduction kinetics; differs from chloroplatinic acid in oxidation state, which can affect nucleation and particle-size control strategies.
Metal-salt precursor (Ni)	7791-20-0	N112126	Nickel(II) chloride hexahydrate	Premium grade, ≥98%	Ni source for catalysts/precursors (Ni(OH)₂, NiSₓ, NiMo*, etc.); residual Cl⁻ may introduce corrosion or side effects, so thorough washing is typically needed after synthesis.
Metal-salt precursor (Ni, high purity)	13478-00-7	N108888	Nickel(II) nitrate hexahydrate (explosive precursor)	PrimorTrace™, ≥99.999% metals basis	Ultra-high-purity Ni source for electrocatalysis studies requiring strict control of trace impurities; nitrates have strong oxidizing/risk attributes.
Metal-salt precursor (Co)	10026-22-9	C431137	Cobalt(II) nitrate hexahydrate	For analysis, premium grade	Co source for cobalt-based catalyst precursors (Co(OH)₂/CoOₓ, CoSₓ, CoP, etc.); nitrate decomposes readily upon heating and is commonly used in calcination/conversion routes.
Metal-salt precursor (Mo)	10102-40-6	S320063	Sodium molybdate dihydrate	For plant cell culture, ≥99.5%	Typical Mo source (MoO₄²⁻); used to prepare Mo-based precursors/composites (e.g., Ni–Mo systems, MoSₓ precursors), enabling homogeneous mixing in aqueous routes.
Metal-salt precursor (Mo)	12054-85-2	A116376	Ammonium molybdate tetrahydrate	For cell culture / insect cell culture, MoO₃ 81–83%	Common soluble Mo source; used in impregnation/co-precipitation/hydrothermal routes to obtain MoOₓ/MoSₓ or Ni/Co composite precursors.
Mo–S single-source precursor	15060-55-6	A1500798	Ammonium tetrathiomolybdate	Moligand™, 10 mM in DMSO	Typical Mo+S single-source precursor: used for impregnation/coating and thermal conversion to MoSₓ (further convertible to MoS₂), or for building NiMoS/CoMoS-like precursor systems with Ni/Co.
Metal precursor (W source)	10213-10-2	S431261	Sodium tungstate dihydrate	Suitable for preparing protein-free filtrates by Folin method	Soluble W source: starting point for W-based material precursors (WOₓ/WSₓ/WC routes), also used for compositing/doping and impregnation loading.

C. Conversion/Doping Reagents & Additives (S/P/N Sources, Reductants, Chelators/Surfactants)

Category	CAS No.	Aladdin Cat. No.	Name	Spec / Purity	Product features / role (HER-related)
N source / precipitation aid	57-13-6	U432962	Urea	Beads	Often used as a mild precipitation/morphology-control additive (releases NH₃/CO₂ upon heating to promote uniform formation of metal hydroxide/carbonate precursors); also used as an N-doped carbon precursor/additive.
N source / framework precursor	108-78-1	T431382	2,4,6-Triamino-1,3,5-triazine	For synthesis	Common nitrogen-rich precursor (for g-C₃N₄ or N-doped carbon/composite supports); used to tune electronic structure and the local environment of active sites.
S source / coordination additive	62-56-6	T112512	Thiourea	Premium grade, ≥99%	Common sulfidation and coordination/slow-release sulfur source: generates metal sulfides (NiSₓ/CoSₓ/MoSₓ, etc.) in hydro/solvothermal routes and helps morphology control; can also contribute N/S doping.
S source / slow-release sulfidating agent	62-55-5	T118452	Thioacetamide	ACS, ≥99%	Classic “slow-release sulfur source”: gradually releases sulfide/sulfur species under heating/hydrothermal conditions, favoring uniform metal sulfide nanostructures.
S source / reductive aid	10102-17-7	S431245	Sodium thiosulfate pentahydrate	Ph.Eur, for analysis, ACS, premium grade	Can serve as a mild reductant/chelating component; in some syntheses used as a sulfur-containing precursor/sulfur source or to modulate sulfidation (route-dependent).
S source / sulfiding agent	1313-84-4	S116078	Sodium sulfide nonahydrate	PrimorTrace™, ≥99.99% metals basis	Strong S²⁻ source for precipitation/sulfidation to form metal sulfides or for post-sulfidation; readily oxidized by air and absorbs CO₂—prepare quickly and store sealed.
S source / sulfiding agent	1313-82-2	S138149	Sodium sulfide	≥95%	Basic S²⁻ sulfiding/precipitating agent; commonly used for rapid metal sulfide formation or post-sulfidation. With lower purity grades, trace-impurity background deserves more attention.
P source / reductant	10039-56-2	S475687	Sodium hypophosphite monohydrate	Ph.Eur, puriss. p.a., ≥99%	Common phosphidation/reduction precursor for metal phosphides (NiP/CoP, etc.) or reductive deposition; heating may generate strongly reducing phosphorus-containing gases—strict safety and exhaust handling are required.
Strong reductant (for synthesis)	16940-66-2	S432207	Sodium borohydride (explosive precursor)	purum p.a., ≥96% (gas-volumetric)	Common strong reductant for rapid reduction of metal precursors (Pt/Ni/Co nanoparticles, supported deposition, etc.); releases H₂ and is water/acid sensitive—control addition and safety strictly.
Chelator / complexing agent	6381-92-6	E118596	Disodium EDTA dihydrate	For plant cell culture, ≥99%	Chelates metal ions to control impurities, stabilize solutions, or tune metal-ion activity; can also affect deposition/nucleation—controls are important.
Complexing / morphology-control additive	77-92-9	C774600	Citric acid	Anhydrous, PharmPure™, USP/JP/BP/Ph.Eur, pharmaceutical grade, powder	Coordinates and buffers metal-ion release to control morphology/particle size; common in sol–gel/co-precipitation/polyol routes; can also improve slurry stability (controls recommended).
Dispersant / stabilizer (polymer)	9003-39-8	P434444	Poly(vinylpyrrolidone) (PVP)	For plant cell culture, avg. MW 10,000	Nanoparticle stabilizer/dispersant for metal nanoparticle synthesis and ink stability, improving coating uniformity; may also block active sites—use “with/without PVP” controls.
Surfactant / dispersant (anionic)	151-21-3	S432158	Sodium dodecyl sulfate (SDS)	For electrophoresis, anionic	Strong dispersing/wetting agent to improve powder dispersion and coating uniformity in aqueous systems; may alter electrode wetting and interfacial charge—blank controls recommended.
Surfactant / dispersant (cationic)	57-09-0	H108983	Cetyltrimethylammonium bromide (CTAB)	≥99%	Cationic surfactant for morphology control, templating/coating, and dispersion; may adsorb strongly and affect electrochemical interfaces—use “with/without CTAB” controls and wash thoroughly.

D. Electrolytes / Buffers / Supporting Salts (Electrolyte Preparation and Reference Systems)

Category	CAS No.	Aladdin Cat. No.	Name	Spec / Purity	Product features / role (HER-related)
Acidic electrolyte / cleaning acid	7664-93-9	S485807	Sulfuric acid (controlled precursor)	Premium grade, for analysis, ≥98%	One of the common acidic HER electrolytes; also used for electrode/glassy carbon cleaning and activation (strongly corrosive; regulated precursor attributes).
Acidic electrolyte (weakly coordinating anion)	7601-90-3	P433647	Perchloric acid (explosive precursor)	For analysis (max. 0.0000005% Hg column), premium grade, ACS/ISO/Reag., Ph.Eur	Strong acid with weakly coordinating ClO₄⁻, often used as an acidic HER reference electrolyte to minimize specific adsorption; however, it poses strong oxidizing/explosion hazards and requires strict safety compliance.
Acidic electrolyte / cleaning acid	7647-01-0	H485680	Fuming hydrochloric acid 37% (controlled precursor)	Premium grade, for analysis, max. 0.001 ppm Hg	Common acid for acidic-electrolyte testing and cleaning/activation; Cl⁻ may introduce corrosion/specific adsorption effects—note differences vs H₂SO₄/HClO₄ in mechanistic controls.
Alkaline electrolyte / base	1310-73-2	S111498	Sodium hydroxide	Premium grade, ≥96%	Alkaline HER electrolyte (or pH adjustment); readily absorbs CO₂ and forms carbonates—pay attention to sealing and freshness in preparation/storage.
Alkaline electrolyte / high-purity base	1310-58-3	P431767	Potassium hydroxide	Anhydrous, ≥99.95% metals basis	Preferred high-purity alkaline HER electrolyte to reduce trace-metal effects; also absorbs CO₂—manage solution preparation/storage accordingly.
Supporting electrolyte / reference-electrode salt	7447-40-7	P112144	Potassium chloride	For cell culture, ≥99.5%	Commonly used in reference electrode (Ag/AgCl) filling solutions/salt bridges or for conductivity control; generally not used as the primary HER electrolyte.
Supporting electrolyte (inert salt)	7757-82-6	S112289	Sodium sulfate (anhydrous)	For plant cell culture, ≥99%	Inert supporting electrolyte for controlling ionic strength/conductivity and as a “non-specific anion” reference (often milder than Cl⁻/PO₄³⁻).
Supporting electrolyte (inert salt)	7778-80-5	P112586	Potassium sulfate	For plant cell culture	Inert supporting electrolyte (K⁺ system); used for ionic-strength controls or to avoid Na⁺-specific differences.
Buffer salt / near-neutral system (phosphate)	7778-77-0	P113042	Potassium dihydrogen phosphate	For plant cell culture, ≥99%	Paired with K₂HPO₄ to form phosphate buffers (PBS/phosphate buffer) for near-neutral HER or mechanistic controls; phosphate may adsorb/affect interfaces—compare against borate/sulfate where appropriate.
Buffer salt / near-neutral system (phosphate)	7758-11-4	D433945	Dipotassium hydrogen phosphate (anhydrous)	Anhydrous, premium grade, for analysis	Paired with KH₂PO₄ to form phosphate buffers (K⁺ system); analytical grade is suitable for electrochemical controls and mechanistic data.
Buffer salt / near-neutral system (phosphate)	7558-80-7	S108343	Sodium dihydrogen phosphate (anhydrous)	For cell culture / insect cell culture, ≥99% (T)	Paired with Na₂HPO₄ to form phosphate buffers (Na⁺ system); useful for Na⁺/K⁺ ion-identity comparisons.
Buffer salt / near-neutral system (phosphate)	7558-79-4	S118441	Disodium hydrogen phosphate (anhydrous)	For cell culture / insect cell culture	Paired with NaH₂PO₄ to form phosphate buffers; used for near-neutral HER/mechanistic controls and ionic-strength control.
Buffer system (borate)	10043-35-3	B111605	Boric acid	For cell culture / insect cell culture, ≥99.5%	Commonly used to prepare borate buffers for pH buffering and controls in alkaline/near-neutral electrochemistry; also useful for comparing “phosphate vs borate” anion effects.

E. Electrode-Building Materials (Membranes / Binders / Conductive Carbon / Supports)

Category	CAS No.	Aladdin Cat. No.	Name	Spec / Purity	Product features / role (HER-related)
Electrode binder / hydrophobic material	9002-84-0	P434340	Polytetrafluoroethylene (PTFE)	Beads	Inert hydrophobic binder/porogen and hydrophobicity-tuning material; often used for gas diffusion electrodes (GDEs) or to improve corrosion resistance and anti-wetting.
Electrode binder / film-forming	24937-79-9	P1492342	Poly(vinylidene fluoride) (PVDF)	Melt viscosity (K Poise): 23.5–29.5, powder	Common electrode binder (paired with NMP); used for forming films from powder catalysts and improving adhesion and mechanical stability.
Membrane / ion-conducting material	31175-20-9	N432605	Nafion™ perfluorinated membrane	Thickness 0.002 inch	Core PEM material; also used as an ion-conducting binder phase in acidic catalyst inks (lower stability in alkaline environments).
Conductive carbon / support	1333-86-4	C124422	Carbon black	For elemental analysis	Most common conductive additive/support: builds conductive networks, improves electrode conductivity and coating consistency; often used as a conductivity control vs graphene/graphite.
Conductive carbon / functionalized carbon support	7782-42-5	G196556	Carboxylated graphene (nano-size)	Diameter 50–200 nm; single-layer ratio >98%; carboxyl ratio 8.0 wt%	Highly conductive 2D carbon support/additive; carboxyl groups improve hydrophilicity and dispersibility, aiding nanoparticle loading (metals/sulfides/phosphides) and electron transport; often used for “conductive framework/interface engineering” controls.

F. Solvents & Cleaning (Inks / Film Making / Labware)

Category	CAS No.	Aladdin Cat. No.	Name	Spec / Purity	Product features / role (HER-related)
Solvent / electrolyte water	7732-18-5	W433885	Water	MS grade, UltraPureChrom™, UHPLC grade	High-purity water for electrolyte preparation/cleaning/blank controls; minimizes background currents and contamination from trace metals/organics.
Solvent / cleaning	67-63-0	I112023	Isopropanol (IPA)	Preparative chromatography grade, ≥99.8%	Electrode and labware cleaning; often used as a volatile co-solvent in catalyst inks (improves wetting/spreading, accelerates drying).
Solvent / cleaning	64-17-5	E111989	Ethanol	Premium grade, water ≤0.3%	Cleaning and ink co-solvent; paired with water/IPA to improve dispersion and coating uniformity.
Solvent (electrode preparation)	872-50-4	M119668	N-Methyl-2-pyrrolidone (NMP)	Anhydrous, ≥99.5%	Typical electrode-preparation solvent: dissolves PVDF for binder solutions and is used for catalyst slurry/coating; high boiling point—drying and residual-solvent control are important.
Solvent / polyol system	107-21-1	E119700	Ethylene glycol	Anhydrous, ≥99.8%	Common solvent/reaction medium for polyol methods: used for metal nanoparticle formation, dispersion, and coating formulations ; high boiling point—control residual solvent and keep drying conditions consistent.

Note: The above are representative Aladdin catalog numbers. For more specifications, please refer to the full product list at the end of the document, or search the Aladdin website by product name/CAS number.

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