Building a Carbon Credit Trading Platform on Celo


In the face of climate change, innovative technologies like blockchain are being employed to address our environmental impact. In this advanced tutorial, we will walk through the process of building a carbon credit trading platform on the Celo blockchain. Our platform will leverage the capabilities of Solidity, JavaScript, and the Celo SDK, along with the innovative Toucan Protocol for Tokenized Carbon Credits.


This tutorial is designed for developers with a strong understanding of blockchain technology, smart contract development, Solidity, JavaScript, and the Celo SDK. If you’re new to Celo, you might want to first complete the “Connect to Celo using Hardhat” tutorial.


Before we start, make sure you have the following installed:

  1. Metamask: Download and install it from Metamask website.
  2. NodeJS 12.0.1+: If not installed, download from NodeJS website.

We will install other packages as we proceed.

Getting Started with the Carbon Credit Trading Platform

Our platform will have two main components: the smart contracts that will manage the carbon credits and their trading, and the frontend interface for users to interact with our platform.

Setting Up the Development Environment

First, we’ll need to set up a development environment. We’ll use Hardhat, a development tool for compiling, deploying, testing, and debugging Solidity code.

  • Create a new directory for your project and navigate into it:
mkdir celo-carbon-credit
cd celo-carbon-credit
  • Initialize a new Node.js project:

npm init -y

  • This will create a new package.json file. Next, install Hardhat:

npm install --save-dev hardhat

  • Then, initialize Hardhat:

npx hardhat

This will create a hardhat.config.js file and a scripts and test directory.

Creating the Smart Contracts

Our platform will have two main smart contracts: CarbonCredit and Marketplace.

The CarbonCredit Contract

The CarbonCredit contract will handle the issuance of carbon credits. Each carbon credit represents the reduction of one tonne of CO2 equivalent from the atmosphere. This contract will mint new carbon credits when a verified carbon reduction event occurs.

Create a new file in the contracts directory named CarbonCredit.sol and add the following code:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract CarbonCredit is ERC20 {
    address public admin;

    constructor() ERC20("CarbonCredit", "CC") {
        admin = msg.sender;

    function mint(address to, uint amount) external {
        require(msg.sender == admin, "only admin");
        _mint(to, amount);

In this contract, we’re creating a new ERC20 token named CarbonCredit with a symbol of CC. We also have an admin address that is set to the address that deploys the contract. Only the admin can mint new tokens, simulating the issuance of new carbon credits.

The Marketplace Contract

The Marketplace contract will manage the trading of these carbon credits. This contract will maintain a listing of available carbon credits for sale, allow users to list their carbon credits for sale, and facilitate transactions between buyers and sellers.

Create a new file in the contracts directory named Marketplace.sol and add the following code:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "./CarbonCredit.sol";

contract Marketplace {
    CarbonCredit public token;
    address public admin;
    uint256 public percentFee;

    struct Sale {
        address seller;
        uint256 amount;
        uint256 pricePerToken;
        bool isCompleted;

    Sale[] public sales;

    constructor(address tokenAddress, uint256 fee) {
        require(fee <= 100, "fee too high");
        token = CarbonCredit(tokenAddress);
        admin = msg.sender;
        percentFee = fee;

    function listTokens(uint256 amount, uint256 pricePerToken) external {
        require(token.balanceOf(msg.sender) >= amount, "not enough tokens");
        token.transferFrom(msg.sender, address(this), amount);
            seller: msg.sender,
            amount: amount,
            pricePerToken: pricePerToken,
            isCompleted: false

    function buyTokens(uint256 saleId) external payable {
        Sale storage sale = sales[saleId];
        require(!sale.isCompleted, "sale already completed");
        require(msg.value == sale.pricePerToken * sale.amount, "wrong value sent");

        sale.isCompleted = true;
        uint256 fee = (msg.value * percentFee) / 100;
        payable(sale.seller).transfer(msg.value - fee);
        token.transfer(msg.sender, sale.amount);

In this contract, we first import the CarbonCredit contract and set up a new ERC20 token. We also set up an admin address and a percentFee that the marketplace will take from each sale.

We then define a Sale struct that represents a sale of carbon credits on our marketplace. Each Sale has a seller, amount of carbon credits for sale, pricePerToken, and a flag isCompleted to indicate whether the sale is complete.

In the constructor, we set the token, admin, and percentFee.

We then have two functions, listTokens and buyTokens. listTokens allows a user to list a certain amount of their carbon credits for sale at a specified price per token. buyTokens allows a user to buy carbon credits from a listed sale.

Now, let’s dive deeper into the functionality of these smart contracts.

Understanding the CarbonCredit Contract

The CarbonCredit contract is a simple contract that creates a new ERC20 token named CarbonCredit with the symbol CC. The contract has an admin address which is set to the address that deploys the contract.

The mint function allows the admin to mint new tokens. This simulates the issuance of new carbon credits when a verified carbon reduction event occurs. The mint function takes two arguments: the address to mint the tokens to, and the amount of tokens to mint. It first checks that the caller of the function is the admin, then calls the internal _mint function to mint the tokens.

This contract represents the tokenization of carbon credits on the blockchain. Each token represents a specific amount of carbon that has been removed from the atmosphere. This token can then be traded, sold, or retired.

Understanding the Marketplace Contract

The Marketplace contract is a bit more complex. It starts by importing the CarbonCredit contract and setting up an instance of it, along with an admin address and a percentFee. The percentFee is the fee that the marketplace takes from each sale.

The contract then defines a Sale struct. This represents a sale of carbon credits on the marketplace. Each Sale includes the seller address, the amount of tokens being sold, the pricePerToken, and a isCompleted flag to indicate if the sale has been completed.

The constructor for this contract sets up the token, admin, and percent fee.

The listTokens function allows users to list their carbon credits for sale on the marketplace. It first checks that the user has enough tokens to list, then transfers the tokens from the user to the contract. It then creates a new Sale and adds it to the sales array.

The buyTokens function allows users to buy tokens from a listed sale. It first checks that the sale is not already completed, and that the value sent with the transaction matches the total price of the tokens. It then marks the sale as completed, calculates the fee for the marketplace, and transfers the fee to the admin and the remaining amount to the seller. Finally, it transfers the tokens from the contract to the buyer.

This contract represents the marketplace where carbon credits can be traded. Users can list their carbon credits for sale, and other users can buy them. The marketplace takes a fee from each sale.

Integrating the Toucan Protocol

Integration with the Toucan Protocol involves understanding the TCO2 token mechanism and the trading process.

npm install @toucanprotocol/contracts

After installing the Toucan Protocol’s smart contract package, we can leverage the TCO2 token mechanism.

import "@toucanprotocol/contracts/TCO2.sol";

contract CarbonCreditPlatform is TCO2 {
    function buyCarbonCredits(address buyer, uint256 amount) public payable {
        _transfer(buyer, amount);
    function sellCarbonCredits(address seller, uint256 amount) public {
        _transferFrom(seller, address(this), amount);

This contract inherits the TCO2 contract from the Toucan Protocol and includes functions for buying and selling carbon credits.

Building the Frontend with JavaScript

Now that we have the smart contract, let’s move on to creating the frontend of our dApp. We’ll use Express.js, a fast, unopinionated, and minimalist web framework for Node.js, and the Celo SDK.

First, we’ll create a new server.js file and add the following code to start an Express server:

const express = require('express');
const app = express();
const port = 3000;

app.get('/', (req, res) => res.send('Welcome to the Carbon Credit Trading Platform!'));

app.listen(port, () => console.log(`Server is running on http://localhost:${port}`));

Now, if you navigate to http://localhost:3000 in your web browser, you should see the message “Welcome to the Carbon Credit Trading Platform!”

Connecting to the Celo Network

Next, we will connect our app to the Celo network using the Celo SDK. We will add the following code in our server.js file:

const Web3 = require('web3');
const ContractKit = require('@celo/contractkit');

let web3 = new Web3('');
let kit = ContractKit.newKitFromWeb3(web3);

Make sure to replace ‘’ with your own Celo node URL.

Interacting with the Smart Contract

Our next step is to interact with our Carbon Credit smart contract. We will create functions that issue, trade, and retire carbon credits:

const contractAddress = 'Your_Contract_Address_Here';  // Replace with your deployed contract address

let carbonCredit = new web3.eth.Contract(abi, contractAddress);

// Issue Carbon Credits
app.get('/issue', async (req, res) => {
    let issue = await carbonCredit.methods.issue('account_address', amount).send({ from: 'account_address' });

// Trade Carbon Credits
app.get('/trade', async (req, res) => {
    let trade = await carbonCredit.methods.transfer('receiver_address', amount).send({ from: 'sender_address' });

// Retire Carbon Credits
app.get('/retire', async (req, res) => {
    let retire = await carbonCredit.methods.retire('account_address', amount).send({ from: 'account_address' });

Replace ‘account_address’, ‘receiver_address’, and ‘sender_address’ with appropriate Ethereum addresses. The amount should be the amount of carbon credits to be issued, traded, or retired.

Integrating the Marketplace in our Frontend

Let’s integrate the marketplace into our frontend by adding more routes to our server.js file:

const marketplaceAddress = 'Your_Marketplace_Contract_Address_Here';  // Replace with your deployed marketplace contract address

let marketplace = new web3.eth.Contract(abi, marketplaceAddress);

// Buy Carbon Credits
app.get('/buy', async (req, res) => {
    let buy = await marketplace.methods.buyCarbonCredits('buyer_address', amount).send({ from: 'buyer_address', value: web3.utils.toWei(amount.toString(), "ether") });

// Sell Carbon Credits
app.get('/sell', async (req, res) => {
    let sell = await marketplace.methods.sellCarbonCredits('seller_address', amount).send({ from: 'seller_address' });

Replace buyer_address and seller_address with the appropriate Ethereum addresses, and amount with the amount of carbon credits to be bought or sold.


Congratulations! You have just built an advanced carbon credit trading platform on the Celo blockchain. This platform uses the power of Solidity, JavaScript, the Celo SDK, and the Toucan Protocol for tokenized carbon credits, to issue, trade, and retire carbon credits efficiently.

Next Steps

To continue building on what you’ve learned, you might consider adding more features such as a user authentication system, a better user interface for interacting with the smart contracts, or even exploring other token standards.

Additionally, you can explore more about the Celo SDK and the Toucan Protocol.

About the Author

Oluwalana is a blockchain developer and technical writer, experienced in creating decentralized applications on Ethereum and Celo platforms. With a passion for knowledge-sharing, Oluwalana has authored various tutorials and articles on blockchain and other emerging technologies. Follow me on Twitter for insights on blockchain and emerging tech. For professional inquiries, kindly connect witth me on LinkedIn and explore my work on GitHub.


This tutorial was built with the help of the following resources:


I think your proposal is great. I look forward to it.


Nice idea


This is the first proposal I’ll ever see on Carbon credit. I’m very interested in its implementation. For my suggestion, I sent you in dm.


Thank you, i have responded

I am thinking on starting a Pathway focused on Carbon Credit and ReFi

Would be working with Celo, but also considering how i can infuse Toucan as well


That would not be a bad idea if you have a clear pathway for it.


this is real life use case and a very important one at that , looking forward to this.


Fantastic news! Your proposal has landed in this week’s top voted list. As you begin your project journey, remember to align with our community and technical guidelines, ensuring a high quality platform for our developers. Congratulations! :mortar_board: :seedling:

Note: @Lanacreates we’d like to move forward with this request given the number of votes. Can you revise the stack to incorporate a technology such as Toucan Protocol for Tokenized Carbon Credits so that it provides an introduction to our most recent technologies. Kindly revise the article, and once you are ready, we will conduct an additional review and proceed with rewarding you for this tutorial. Thank you!


Hi @Celo_Academy
The article stack and description has been updated, kindly review so i can proceed with writing this tutorial. Thank you!


Thanks! approved for you to get started whenever you’d like :mortar_board::seedling:

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Hi @Lanacreates I’ll be reviewing your piece in 1 to 2 days

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