Carbon capture, hydrogen economy (electrolysis, fuel cells)

5.5.5 · Chemistry › Green Chemistry & Sustainability

1. Carbon Capture

KYA hain main routes?

Post-combustion: jalane ke baad flue gas se $CO_{2}$ scrub karo.
Pre-combustion: pehle fuel ko $CO_{2}$ + $H_{2}$ mein convert karo, $CO_{2}$ hatao, phir $H_{2}$ jalao.
Direct Air Capture (DAC): seedha ambient air se $CO_{2}$ kheecho (mushkil hai — sirf ~0.04% $CO_{2}$ hoti hai).

2. The Hydrogen Economy — hydrogen ke colours

3. Electrolysis of Water (energy store karna → H₂ banana)

Half-reactions scratch se derive karo. Paani electrons gain ya lose kar sakta hai:

Cathode par (reduction, $e^{-}$ gain karta hai): hydrogen nikalti hai.
Anode par (oxidation, $e^{-}$ lose karta hai): oxygen nikalti hai.

Acidic / neutral solution mein: $Cathode: 2 H^{+} + 2 e^{-} \to H_{2} (E^{\circ} = 0.00 V)$ $Anode: 2 H_{2} O \to O_{2} + 4 H^{+} + 4 e^{-} (E^{\circ} = + 1.23 V)$

4. Fuel Cell (electricity banana → H₂ energy release karna)

Figure — Carbon capture, hydrogen economy (electrolysis, fuel cells)

Forecast-then-Verify

Recall Padhne se pehle predict karo: agar electrolysis mein current double karo, to

$H_{2}$ production ki rate kya hogi? Wo bhi double ho jaayegi. Moles of $H_{2} \propto$ charge $= I \times t$ . Double $I$ → har second double charge → har second double $H_{2}$ .

Recall Predict karo: kya fuel-cell voltage Carnot efficiency par depend karta hai?

Nahi — fuel cells heat engines nahi hain, isliye Carnot unhe cap nahi karta. Yahi to poora advantage hai.

Common Mistakes (Steel-manned)

Active Recall — #flashcards/chemistry

What does CCS stand for and do?

Carbon Capture and Storage — CO₂ ko gas stream se alag karo aur ise permanently underground store karo.

Amine CO₂ capture reversible kyu hai?

Absorption exothermic hai isliye thanda ise favour karta hai; garam karne par ye reverse ho jaata hai (Le Chatelier), pure CO₂ release hoti hai aur amine regenerate ho jaati hai.

CO₂ amine se bind karne ki acid–base wajah?

CO₂ ek mild acid (acid anhydride) hai; amine ek base hai jo ise neutralise karti hai.

Green vs grey vs blue hydrogen?

Green = renewable power se electrolysis; grey = methane ki steam reforming (CO₂ emit karta hai); blue = grey + carbon capture.

Water electrolysis (acidic) mein cathode half-reaction?

2H⁺ + 2e⁻ → H₂.

Water electrolysis (acidic) mein anode half-reaction?

2H₂O → O₂ + 4H⁺ + 4e⁻.

Paani electrolyse karne ka minimum theoretical voltage aur kyu?

1.23 V, paani banane ke liye E° = −ΔG°/nF se.

Real electrolysis voltage 1.23 V se zyada kyu hoti hai?

Overpotential aur internal resistance kinetic energy cost add karte hain.

Overall fuel-cell reaction aur uska E°?

H₂ + ½O₂ → H₂O, E° = +1.23 V (spontaneous).

Fuel cells combustion-engine efficiency se better kyu hain?

Ye chemical energy ko seedha electricity mein convert karte hain, heat engines ke Carnot limit se bachte hue.

Har H₂ molecule produce karne mein kitne electrons lagte hain?

2 electrons.

Electrolysis aur fuel cell ka relation?

Same redox reaction ulta; ΔG aur voltage ka sign flip ho jaata hai.

Recall Feynman: 12-saal ke bacche ko samjhao

Paani do hydrogen hain jo ek oxygen se chipke hain. Agar tum paani mein se electricity push karo, tum inhe alag kar sakte ho — ek wire par hydrogen gas ke bubbles, doosre par oxygen. Ye ek battery charge karne jaisa hai: tumne energy hydrogen mein store kar li. Baad mein, fuel cell mein, tum hydrogen aur oxygen ko wapas milne dete ho — phir se paani banta hai aur tumhe electricity milti hai, jaise battery discharge ho rahi ho. Cool part yeh hai: ek hi "exhaust" hai aur wo hai paani. Alag se, smokestacks saaf karne ke liye, hum smoke ko ek special liquid (amine) se dhote hain jo CO₂ gas ko sponge ki tarah pakad leta hai, phir hum sponge ko garam karte hain CO₂ wapas squeeze karne ke liye aur use zameen mein daba dete hain.

Connections

Electrochemistry — Standard Electrode Potentials
Gibbs Free Energy and Spontaneity
Le Chatelier's Principle
Acids, Bases and Anhydrides
Faraday's Laws of Electrolysis
Carnot Cycle and Engine Efficiency
Green Chemistry — 12 Principles
Steam Reforming and Industrial H2